Device and method for optically surveilling at least one area

ABSTRACT

Described herein is a device for optically surveilling at least one area. The device includes a sender unit and a receiver unit. The sender unit has at least one illumination source. The illumination source is designed to generate at least one light beam having a beam profile. Each light beam is designated for propagating to the receiver unit, thereby traversing at least one area for surveillance. The receiver unit includes
         at least one transfer device,   at least two optical sensors, and   at least one evaluation device

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 17/263,977, filed Jan. 28, 2021, which is a U.S.National Phase Application of International Patent Application No.PCT/EP19/71132, filed Aug. 6, 2019, which claims the benefit of priorityto European Patent Application No. 18187676.4, filed Aug. 7, 2018, theentire contents of which are hereby incorporated by reference herein.

DESCRIPTION Field of the Invention

The invention relates to a device for optically surveilling at least onearea, a method for optically surveilling at least one area and varioususes of the device. The device, methods and uses according to thepresent invention specifically may be employed for example for securitytechnology, specifically, to restrict access to dangerous areas such asmachines. However, other applications are also possible.

Prior Art

Light barriers and light curtains are known which can be used forrestricting access to dangerous areas such as machines. A warning may besent out when the area is entered, or the machine might even be shutdown or sent to a control device, in particular a command may be sent toa machine or further evaluation device. Light barriers typicallycomprise an illumination device that points towards a receiver device.The receiver will be in a first state, such as a safe state, as long asa light beam sent from the illumination device is received. The receiverwill be in a second state, such as a warning state, or shutdown state,if the light beam is not received. The light curtains can have severalsender or receiver light beams in order to cover an area such as anentrance to a machine. The light curtain may use reflective elementssuch that sender and receiver can be placed next to each other or inorder to use fewer sender or receiver units.

Light curtains are required by safety norms to be designed as such thatthey will recognize manipulations. For example, safety norm IEC 61496-2requires that the light curtain cannot receive light that takes anindirect route from sender to receiver. For example, a redirection ofthe light beam using mirrors should be recognized by the light curtain.Further, an accidental redirection of the light beam due to shiny metalparts needs to be recognized by the light curtain.

Typical manipulations result from willful manipulations or notintentional manipulations. Willful manipulations may be made to make amachine more productive, if a safety unit such as a light curtain causesregular shut downs. Not intentional manipulations may be changes in themachine setup without noting that the safety unit is concerned.

Various approaches have been proposed to improve safety of lightcurtains. For example, small apertures in sender and receiver units maybe used to make manipulations and changes less likely. However, this mayresult in that setting up the light curtain is more difficult,especially if infrared light is used in the illumination. In a furtherexample, small apertures may be used in the receiver unit such that thereceiver receives only light beams from the direction of theillumination device. To simplify the set-up phase of the sender andreceiver unit relative to each other larger apertures and less collimatelight beams may be used in the sender unit. However, this may reducesafety.

U.S. Pat. No. 7,667,185 B2 describes an optoelectronic sensor assemblywith at least one light emitter and at least one light receivercomprising a spatially resolving receiving element, with the receivingelement having an inner region comprising at least one photosensitiveelement for detecting the light beam and an outer region comprising atleast one photosensitive element for determining the position of thelight beam emitted by the light emitter, with the outer regionsatisfying lower sensitivity and/or bandwidth requirements than theinner region.

US 2008/173831 A1 describes an optoelectronic sensor for detectingobjects in a monitored region which has light emitters and associatedlight receivers adjustably arranged relative to each other so that lightemitted by the light emitter is directly received by the light receiver.The light emitter and the light receiver conform to normed requirementswhich define a normed region that is free of reflecting surfaces so thatlight emitted by the light emitter which passed beyond the normed regioncannot be received by the light receiver due to a reflection of suchlight. In the normed region, an emitted light cone generated by thelight emitter and a received light cone defined by the light receiveroverlap within a normed opening angle. An evaluation unit interprets theinterruption in the light directed to the light receiving element as adetection of an object in the monitored region. The light emitter formsan emitted light cone with an opening angle of any desired magnitude,while the light receiver has a received light cone with an opening angleof no more than one-half of the normed opening angle.

In a further example, the light curtain may be combined with a distancemeasurement such as a time-of-flight measurement. However, this willrequire a synchronized direct coupling of sender and receiver unit. DE10 2016 122 364 A1 describes an optoelectronic sensor, in particularlight curtain, for monitoring a surveillance area, wherein the sensorcomprises at least one light transmitter for emitting a surveillancebeam, at least one light receiver for receiving the surveillance beamand generating a corresponding received signal and an evaluation unit,in order to detect from the received signal if the surveillance beam isinterrupted and to issue an interrupt signal upon detecting of aninadmissible interruption of the surveillance beam. In this case, thelight receiver is configured such that the received signal depends fromthe geometry of the generated light spot of the surveillance beam on thelight receiver, and the evaluation unit is configured to detect from thereceived signal whether the uninterrupted surveillance beam ismanipulated. However, the bandwidth of such light receivers is oftenlimited and modulation patterns other than 50:50 rectangular patternsmay influence the performance of the device and may restrict the use forfast encoded modulations as commonly used in light curtains or lightbarriers. 50:50 rectangular modulation patterns are often not optimalfor industry safety environments as further unrelated devices may emitthese patterns and may therefore manipulate the light curtains.

Problem Addressed by the Invention

It is therefore an object of the present invention to provide devicesand methods facing the above-mentioned technical challenges of knowndevices and methods. Specifically, it is an ob-ject of the presentinvention to provide devices and methods which improve safety such aspreventing manipulations, preferably with a low technical effort andwith low requirements in terms of technical resources and cost.

SUMMARY OF THE INVENTION

This problem is solved by the invention with the features of theindependent patent claims. Advantageous developments of the invention,which can be realized individually or in combination, are presented inthe dependent claims and/or in the following specification and detailedembodiments.

As used in the following, the terms “have”, “comprise” or “include” orany arbitrary grammatical variations thereof are used in a non-exclusiveway. Thus, these terms may both refer to a situation in which, besidesthe feature introduced by these terms, no further features are presentin the entity described in this context and to a situation in which oneor more further features are present. As an example, the expressions “Ahas B”, “A comprises B” and “A includes B” may both refer to a situationin which, besides B, no other element is present in A (i.e. a situationin which A solely and exclusively consists of B) and to a situation inwhich, besides B, one or more further elements are present in entity A,such as element C, elements C and D or even further elements.

Further, it shall be noted that the terms “at least one”, “one or more”or similar expressions indicating that a feature or element may bepresent once or more than once typically will be used only once whenintroducing the respective feature or element. In the following, in mostcases, when referring to the respective feature or element, theexpressions “at least one” or “one or more” will not be repeated,non-withstanding the fact that the respective feature or element may bepresent once or more than once.

Further, as used in the following, the terms “preferably”, “morepreferably”, “particularly”, “more particularly”, “specifically”, “morespecifically” or similar terms are used in conjunction with optionalfeatures, without restricting alternative possibilities. Thus, featuresintroduced by these terms are optional features and are not intended torestrict the scope of the claims in any way. The invention may, as theskilled person will recognize, be performed by using alternativefeatures. Similarly, features introduced by “in an embodiment of theinvention” or similar expressions are intended to be optional features,without any restriction regarding alternative embodiments of theinvention, without any restrictions regarding the scope of the inventionand without any restriction regarding the possibility of combining thefeatures introduced in such a way with other optional or non-optionalfeatures of the invention.

In a first aspect of the present invention a device for opticallysurveilling at least one area is disclosed. The area may be a dangerousarea and/or a surveillance area. As used herein, the ter “surveillancearea” or “area for surveillance” refers to an arbitrary area of interestwhich is and/or needs to be monitored, for example due to safetyreasons. Specifically, the device may be or may comprise at least onelight barrier such at least one light curtain for surveilling at leastone surveillance area. As used herein, the term “light barrier” has itsordinary meaning and specifically, refers to a device configured todetermine one or more of a distance, absence, presence of an object byusing a sender unit and receiver unit. The term light barrier alsorelates to determining presence or absence of the receiver unit, thesender unit or the reflective target. The light barrier may be areflective or one-way device. For example, in a one-way device, thelight barrier may comprise the receiver unit located within theline-of-sight of the sender unit. Thus, an object such as a human orpart of a human may be detected when the light beam is prevented fromgetting to the receiver unit. For example, in a reflective light barrierthe sender unit and the receiver unit may be arranged at the samelocation and the light barrier comprises in addition a reflective targetto reflect the light beam generated by the sender unit back to thereceiver unit. Thus, an object may be detected when the light beam doesnot reach the receiver unit. The light barrier may be using at least onelight beam or a plurality of light beams such as an array of light beamsof a light curtain. The light barrier may be designed as proximitysensor. Borders of the area of surveillance may be defined for one-waydevices by a position of the sender unit and the receiver unit or forreflective devices by a position of the reflective target and the senderand receiver units. For example, the area may be a machine or an area ofthe machine such as a dangerous area of the machine. The area may be anaccess area, for example an access area to a machine. As used herein,the term “optically surveilling” refers to monitoring and/or observingand/or controlling the area using at least one light beam.

The device comprises a sender unit and a receiver unit. The sender unithas at least one illumination source. The illumination source isdesigned to generate at least one light beam having a beam profile. Eachlight beam is designated for propagating to the receiver unit, therebytraversing at least one area for surveillance. The receiver unitcomprises

-   -   at least one transfer device, wherein the transfer device has at        least one focal length in response to the at least one incident        light beam propagating from the illumination source to at least        two optical sensors, wherein the transfer device has an optical        axis, wherein the transfer device constitutes a coordinate        system, wherein a longitudinal coordinate I is a coordinate        along the optical axis and wherein d is a spatial offset from        the optical axis,    -   at least two optical sensors, wherein each optical sensor has at        least one light sensitive area, wherein each optical sensor is        designed to generate at least one sensor signal in response to        an illumination of its respective light-sensitive area by the        light beam, wherein two of the optical sensors are arranged in a        manner that the light-sensitive areas of the two optical sensors        differ in at least one of: their longitudinal coordinate, their        spatial offset, or their surface areas; and    -   at least one evaluation device, wherein the evaluation device is        being configured for generating an output by monitoring at least        one change of, firstly, the beam profile of the at least one        light beam upon traversing the at least one area of surveillance        by evaluating the sensor signals and, further, of at least one        component of a location of the sender unit, wherein the        component is determined with respect to the coordinate system of        the transfer device, by evaluating a combined signal Q from the        sensor signals.

As used herein, the term “sender unit” refers to at least one deviceconfigured for sending and/or transmitting at least one signal,specifically the at least one light beam. As used herein, the term“illumination source” refers to at least one device configured forgenerating at least one light beam. The illumination source may be ormay comprise at least one light source. The light source may be or maycomprise at least one multiple beam light source. For example, the lightsource may comprise at least LED or at least one laser source and atleast one transfer device or one or more diffractive optical elements(DOEs). As used herein, the term “ray” generally refers to a line thatis perpendicular to wavefronts of light which points in a direction ofenergy flow. As used herein, the term “beam” generally refers to acollection of rays. In the following, the terms “ray” and “beam” will beused as synonyms. As further used herein, the term “light beam”generally refers to an amount of light, specifically an amount of lighttraveling essentially in the same direction, including the possibilityof the light beam having a spreading angle or widening angle. The lightbeam may have a spatial extension. Specifically, the light beam may havea non-Gaussian beam profile. The beam profile may be selected from thegroup consisting of a trapezoid beam profile; a triangle beam profile; aconical beam profile. The trapezoid beam profile may have a plateauregion and at least one edge region. As used herein, the term “beamprofile” generally refers to a transverse intensity profile of the lightbeam. The beam profile may be a spatial distribution, in particular inat least one plane perpendicular to the propagation of the light beam,of an intensity of the light beam. The light beam specifically may be aGaussian light beam or a linear combination of Gaussian light beams, aswill be outlined in further detail below. Other embodiments arefeasible, however. The device for optically surveilling may comprise theat least one transfer device configured for one or more of adjusting,defining and determining the beam profile, in particular a shape of thebeam profile.

As used herein, the term “light” generally refers to electromagneticradiation in one or more of the visible spectral range, the ultravioletspectral range and the infrared spectral range. Therein, the termvisible spectral range generally refers to a spectral range of 380 nm to780 nm. The term infrared spectral range generally refers toelectromagnetic radiation in the range of 780 nm to 1 mm, preferably inthe range of 780 nm to 3.0 micrometers. The term ultraviolet spectralrange generally refers to electromagnetic radiation in the range of 1 nmto 380 nm, preferably in the range of 100 nm to 380 nm. Preferably,light as used within the present invention is visible light, i.e. lightin the visible spectral range, or infrared light. The term “light beam”generally may refer to an amount of light emitted and/or reflected intoa specific direction. Thus, the light beam may be a bundle of the lightrays having a predetermined extension in a direction perpendicular to adirection of propagation of the light beam. Preferably, the light beamsmay be or may comprise one or more Gaussian light beams such as a linearcombination of Gaussian light beams, which may be characterized by oneor more Gaussian beam parameters, such as one or more of a beam waist, aRayleigh-length or any other beam parameter or combination of beamparameters suited to characterize a development of a beam diameterand/or a beam propagation in space.

The device for optically surveilling may be configured such that thelight beam propagates from the sender unit towards the receiver unitalong an optical axis of the device for optically surveilling. For thispurpose, the device for optically surveilling may comprise at least onereflective element or reflective target, preferably at least one prism,mirror, reflective foil, retro reflector or the like, for deflecting theilluminating light beam onto the optical axis. Specifically, the devicefor optically surveilling further may comprise at least one reflectivetarget designed for being impinged by the at least one light beampropagating from the at least one illumination source to the at leasttwo optical sensors. The sender unit may comprise at least one controldevice for controlling generating and/or sending the light beam.Alternatively, for reflective light barriers in which the sender unitand the receiver unit may be arranged such that light beam propagatesfrom the sender unit towards a reflective target which reflects thelight beam to the receiver unit. For this purpose, the device foroptically surveilling may comprise at least one reflective target suchas at least one reflective element or retroreflector.

The device for optically surveilling further may comprise a connectionbetween the sender unit and the receiver unit, wherein the connection isdesigned for providing synchronization between the sender unit and thereceiver unit. The synchronization between the sender unit and thereceiver unit may be wire bound and/or may be implemented using at leastone optical synchronization path. Preferably, the connection may be awireless connection such that a wire bound connection is not necessary.The connection between sender and receiver unit may be used fortransmitting monitoring signals to monitor a safe working mode of theillumination source or the sender unit.

Specifically, the illumination source may comprise at least one laserand/or laser source. Various types of lasers may be employed, such assemiconductor lasers. Additionally or alternatively, non-laser lightsources may be used, such as LEDs and/or light bulbs. The illuminationsource may be adapted to generate and/or to project a cloud of points,for example the illumination source may comprise one or more of at leastone digital light processing projector, at least one LCoS projector, atleast one spatial light modulator; at least one diffractive opticalelement; at least one array of light emitting diodes; at least one arrayof laser light sources. The illumination source may comprise anartificial illumination source, in particular at least one laser sourceand/or at least one incandescent lamp and/or at least one semiconductorlight source, for example, at least one light-emitting diode, inparticular an organic and/or inorganic light-emitting diode. As anexample, the light emitted by the illumination source may have awavelength of 300 to 1000 nm, especially 500 to 1000 nm. Additionally oralternatively, light in the infrared spectral range may be used, such asin the range of 780 nm to 3.0 μm. Specifically, the light in the part ofthe near infrared region where silicon photodiodes are applicablespecifically in the range of 700 nm to 1000 nm may be used. On accountof their generally defined beam profiles and other properties ofhandleability, the use of at least one laser source as the illuminationsource is particularly preferred. The illumination source may beintegrated into a housing of the device for optically surveilling.

The light beam traversing the surveillance area may be less collimated,e.g. the light beam may slightly expand with distance from theillumination source, which allows facilitating the setup of the lightbarrier.

The sender unit further may comprise at least one modulation source. Asused herein, the term “modulation source” refers to at least one deviceconfigured for generating at least one modulation pattern. Themodulation source may be configured for generating a modulation patternin a manner that the modulation source impinges the illumination sourceto generate at least one light beam carrying the modulation pattern. Themodulation pattern may be selected from the group consisting of: apseudo random modulation pattern, an Aiken code, a BCD code, a Gillhamcode, a Stibitz code, a one-hot code, and a gray code.

The modulation pattern may be selected from the group consisting of: arectangular pulse pattern, 50:50 rectangular pattern, sinusoidalpattern, periodic pulse patterns. Compared to the optoelectronic sensordescribed in DE 10 2016 122 364 A1 the sender unit may use more complexmodulation patterns to encode the light source. This may allow that thereceiver unit detects the light beam which was send by the sender unit.

The sender unit may comprise at least two illumination sources. Each ofthe illumination sources may be designed for being modulated by anindividual modulation pattern, the individual modulation pattern of twoillumination sources being different with respect to each other. Thesender unit may comprise an individual modulation source for eachillumination source, or wherein the sender unit further comprises amultiplexer being designated for switching an individual impingement ofat least two of the illumination sources by a single modulation source.The evaluation device is designated for assigning an individualmodulation pattern to an individual illumination source.

The illumination source may have a geometrical extend from 1.5·10⁻⁷mm²·sr to 314 mm²·sr, preferable from 1·10⁻⁵ mm²·sr to 22 mm²·sr, morepreferable from 3·10⁻⁴ mm²·sr to 3.3 mm²·sr. The geometrical extent G ofthe illumination source may be defined by G=A·Ω·n², specifically forrotationally-symmetric optical systems with a half aperture angle θ,G=π·A·sin²(θ)·n², wherein A is the area of the surface, which can be anactive emitting surface, a light valve, optical aperture or the area ofa fiber core (OF) with A_(OF)=π·r² _(OF), and Ω is the projected solidangle subtended by the light and n is the refractive index of themedium. For optical fibers the divergence angle is obtained byθ_(max)=arcsin(NA/n), where NA is the maximum numerical aperture of theoptical fiber. For example, the illumination source may have an edgelength of 10 mm and the projected solid angle may be 90°. For example,the illumination source may have an edge length of 3 mm and a projectedsolid angle of 60°. Other embodiments are feasible such as an edgelength of 1 mm and a projected solid angle of 35°.

As used herein, the term “receiver unit” refers to at least one deviceconfigured for receiving the at least one light beam propagating fromthe sender unit to the receiver unit. For receiving the light beam, asoutlined above, the receiver unit comprises at least two opticalsensors. As used herein, an “optical sensor” generally refers to alight-sensitive device for detecting a light beam, such as for detectingan illumination and/or a light spot generated by at least one lightbeam. As further used herein, a “light-sensitive area” generally refersto an area of the respective optical sensor which may be illuminatedexternally, by the at least one light beam, in response to whichillumination the at least one sensor signal is generated. Thelight-sensitive area may specifically be located on a surface of therespective optical sensor. Other embodiments, however, are feasible. Asused herein, the term “at least two optical sensors each having at leastone light sensitive area” refers to configurations with two singleoptical sensors each having one light sensitive area and toconfigurations with one combined optical sensor having at least twolight sensitive areas. Thus, the term “optical sensor” furthermorerefers to a light-sensitive device configured to generate one outputsignal, whereas, herein, a light-sensitive device configured to generatetwo or more output signals, for example at least one CCD and/or CMOSdevice, is referred to as two or more optical sensors. As will furtherbe outlined in detail below, each optical sensor may be embodied suchthat precisely one light-sensitive area is present in the respectiveoptical sensor, such as by providing precisely one light-sensitive areawhich may be illuminated, in response to which illumination preciselyone uniform sensor signal is created for the whole optical sensor. Thus,each optical sensor may be a single area optical sensor. The use of thesingle area optical sensors, however, renders the setup of the receiverunit specifically simple and efficient. Thus, as an example,commercially available photo-sensors, such as commercially availablesilicon photodiodes, each having precisely one sensitive area, may beused in the set-up. Other embodiments, however, are feasible. Thus, asan example, an optical device comprising two, three, four or more thanfour light-sensitive areas may be used which is regarded as two, three,four or more than four optical sensors in the context of the presentinvention. As an example, the optical sensors may comprise a matrix oflight-sensitive areas. Thus, as an example, the optical sensors may bepart of or constitute a pixelated optical device. As an example, theoptical sensors may be part of or constitute at least one CCD and/orCMOS device having a matrix of pixels, each pixel forming alight-sensitive area.

As further used herein, a “sensor signal” generally refers to a signalgenerated by an optical sensor in response to the illumination by thelight beam. Specifically, the sensor signal may be or may comprise atleast one electrical signal, such as at least one analogue electricalsignal and/or at least one digital electrical signal. More specifically,the sensor signal may be or may comprise at least one voltage signaland/or at least one current signal. More specifically, the sensor signalmay comprise at least one photocurrent. Further, either raw sensorsignals may be used, or the receiver unit, the optical sensors or anyother element may be adapted to process or preprocess the sensor signal,thereby generating secondary sensor signals, which may also be used assensor signals, such as preprocessing by filtering or the like.

The light-sensitive areas may be oriented towards the sender unit,specifically for one-way light barriers. As used herein, the term “isoriented towards the sender unit” generally refers to the situation thatthe respective surfaces of the light-sensitive areas are fully orpartially visible from the sender unit. Specifically, at least oneinterconnecting line between at least one point of the sender unit andat least one point of the respective light-sensitive area may form anangle with a surface element of the light-sensitive area which isdifferent from 0°, such as an angle in the range of 20° to 90°,preferably 80 to 90° such as 90°. Thus, when the sender unit is locatedon the optical axis or close to the optical axis, the light beampropagating from the sender unit towards the receiver unit may beessentially parallel to the optical axis. As used herein, the term“essentially perpendicular” refers to the condition of a perpendicularorientation, with a tolerance of e.g. ±20° or less, preferably atolerance of ±10° or less, more preferably a tolerance of ±5° or less.Similarly, the term “essentially parallel” refers to the condition of aparallel orientation, with a tolerance of e.g. ±20° or less, preferablya tolerance of ±10° or less, more preferably a tolerance of ±5° or less.Additionally or alternatively, at least one of the light-sensitive areasmay be oriented differing from an orientation towards the sender unitand the receiver unit may comprise at least one reflective elementand/or at least one optical fiber configured to guide the light beamonto the light-sensitive area.

The sender unit and the receiver unit may be arranged with respect toeach other in a manner that the sensor signal of at least one of theoptical sensors is a highest sensor signal. As used herein, the term“highest” refers to one or both of magnitude or intensity of the sensorsignal. Specifically, the optimal arrangement of the light barrier'szero position may be as such that the sensitivity of the combined signalQ concerning changes in the sensor signal is highest.

The optical sensors may be sensitive in one or more of the ultraviolet,the visible or the infrared spectral range. Specifically, the opticalsensors may be sensitive in the visible spectral range from 500 nm to780 nm, most preferably at 650 nm to 750 nm or at 690 nm to 700 nm.Specifically, the optical sensors may be sensitive in the near infraredregion. Specifically, the optical sensors may be sensitive in the partof the near infrared region where silicon photodiodes are applicablespecifically in the range of 700 nm to 1000 nm. The optical sensors,specifically, may be sensitive in the infrared spectral range,specifically in the range of 780 nm to 3.0 micrometers. For example, theoptical sensors each, independently, may be or may comprise at least oneelement selected from the group consisting of a photodiode, a photocell,a photoconductor, a phototransistor or any combination thereof. Forexample, the optical sensors may be or may comprise at least one elementselected from the group consisting of a CCD sensor element, a CMOSsensor element, a photodiode, a photocell, a photoconductor, aphototransistor or any combination thereof. Any other type ofphotosensitive element may be used. As will be outlined in furtherdetail below, the photosensitive element generally may fully orpartially be made of inorganic materials and/or may fully or partiallybe made of organic materials. Most commonly, as will be outlined infurther detail below, one or more photodiodes may be used, such ascommercially available photodiodes, e.g. inorganic semiconductorphotodiodes. As further used herein, the term “photosensitive element”generally refers to an element which is sensitive against illuminationin one or more of the ultraviolet, the visible or the infrared spectralrange. Specifically, the photosensitive element may be or may compriseat least one element selected from the group consisting of a photodiode,a photocell, a photoconductor, a phototransistor or any combinationthereof. Any other type of photosensitive element may be used.

The optical sensors specifically may be semiconductor sensors,preferably inorganic semiconductor sensors, more preferably photodiodesand most preferably silicon photodiodes. Thus, the present inventionsimply may be realized by using commercially available inorganicphotodiodes, i.e. one small photodiode and one large area photodiode.Thus, the setup of the present invention may be realized in a cheap andinexpensive fashion. Specifically, the optical sensors may be or maycomprise inorganic photodiodes which are sensitive in the infraredspectral range, preferably in the range of 780 nm to 3.0 micrometers,and/or sensitive in the visible spectral range, preferably in the rangeof 380 nm to 780 nm. Specifically, the optical sensors may be sensitivein the part of the near infrared region where silicon photodiodes areapplicable specifically in the range of 700 nm to 1000 nm. Infraredoptical sensors which may be used for the optical may be commerciallyavailable infrared optical sensors, such as infrared optical sensorscommercially available under the brand name Hertzstueck™ from trinamiXGmbH, D-67056 Ludwigshafen am Rhein, Germany. Thus, as an example, theoptical sensors may comprise at least one optical sensor of an intrinsicphotovoltaic type, more preferably at least one semiconductor photodiodeselected from the group consisting of: a Ge photodiode, an InGaAsphotodiode, an extended InGaAs photodiode, an InAs photodiode, an InSbphotodiode, a HgCdTe photodiode. Additionally or alternatively, theoptical sensors may comprise at least one optical sensor of an extrinsicphotovoltaic type, more preferably at least one semiconductor photodiodeselected from the group consisting of: a Ge:Au photodiode, a Ge:Hgphotodiode, a Ge:Cu photodiode, a Ge:Zn photodiode, a Si:Ga photodiode,a Si:As photodiode. Additionally or alternatively, the optical sensorsmay comprise at least one at least one photoconductive sensor such as aPbS or PbSe sensor, a bolometer, preferably a bolometer selected fromthe group consisting of a VO bolometer and an amorphous Si bolometer.The optical sensors may be opaque, transparent or semitransparent. Forthe sake of simplicity, however, opaque sensors which are nottransparent for the light beam, may be used, since these opaque sensorsgenerally are widely commercially available. The optical sensorsspecifically may be uniform sensor having a single light-sensitive area.Thus, the optical sensors specifically may be a non-pixelated opticalsensor.

In view of the technical challenges involved in the prior art documentDE 10 2016 122 364 A1 as discussed above, specifically in view of thetechnical effort which is required for generating the so called FiPeffect as described in WO 2015/024871 it has to be noted that thepresent invention specifically may be realized by using non-FiP opticalsensors. In fact, since optical sensors having the FiP characteristictypically exhibit a strong peak in the respective sensor signals at afocal point, the range of measurement of a receiver unit using FiPsensors as optical sensors may be limited to a range in between the twopositions and which the first and second optical sensors are in focus ofthe light beam. When using linear optical sensors, however, i.e. opticalsensors not exhibiting the FiP effect, this problem, with the setup ofthe present invention, generally may be avoided. Consequently, the firstand second optical sensor may each have, at least within a range ofmeasurement, a linear signal characteristic such that the respectivefirst and second sensor signals may be dependent on the total power ofillumination of the respective optical sensor and may be independentfrom a diameter of a light spot of the illumination. It shall be noted,however, that other embodiments are feasible, too.

The first and second optical sensors each specifically may besemiconductor sensors, preferably inorganic semiconductor sensors, morepreferably photodiodes and most preferably silicon photodiodes. Thus, asopposed to complex and expensive FiP sensors, the present inventionsimply may be realized by using commercially available inorganicphotodiodes, i.e. one small photodiode and one large area photodiode.Thus, the setup of the present invention may be realized in a cheap andinexpensive fashion. However, embodiments are feasible in which thereceiver unit may comprise at least one FiP sensor adapted forgenerating the so called FiP effect as described in WO 2015/024871.

The illumination source and the optical sensors may be arranged in acommon plane or in different planes. The illumination source and theoptical sensors may have different spatial orientation. In particular,the illumination source and the optical sensors may be arranged in atwisted arrangement. The illuminating light beam generally may beparallel to the optical axis or tilted with respect to the optical axis,e.g. including an angle with the optical axis. As an example, theilluminating light beam, such as the laser light beam, and the opticalaxis may include an angle of less than 10°, preferably less than 5° oreven less than 2°. Other embodiments, however, are feasible. Further,the illuminating light beam may be on the optical axis or off theoptical axis. As an example, the illuminating light beam may be parallelto the optical axis having a distance of less than 10 mm to the opticalaxis, preferably less than 5 mm to the optical axis or even less than 1mm to the optical axis or may even coincide with the optical axis.

The receiver unit comprises at least one transfer device. The term“transfer device”, also denoted as “transfer system”, may generallyrefer to one or more optical elements which are adapted to modify thelight beam, such as by modifying one or more of a beam parameter of thelight beam, a width of the light beam or a direction of the light beam.The transfer device may be adapted to guide the light beam onto theoptical sensors. The transfer device specifically may comprise one ormore of: at least one lens, for example at least one lens selected fromthe group consisting of at least one focus-tunable lens, at least oneaspheric lens, at least one spheric lens, at least one Fresnel lens; atleast one aspheric lens; at least one diffractive optical element; atleast one concave mirror; at least one beam deflection element,preferably at least one mirror; at least one beam splitting element,preferably at least one of a beam splitting cube or a beam splittingmirror; at least one multi-lens system. The transfer device may compriseat least one gradient index (GRIN) lens such as GRIN lenses availablefrom Grintech GmbH, Schillerstraße 1, 07745 Jena, Germany. The GRIN lensmay have a continuous refraction gradient, for example, an axial and/orradial and/or spherical refraction gradient. The f-number of the GRINlens may be dependent on a lens length. Using GRIN lens may allowminiaturizing optics, in particular using very thin optics. For example,very thin optics with a thickness or diameter of 0.2 mm may be possible.The transfer device may comprise at least one annular axial lens, forexample torus form. The annular axial lens may have a plano-convex form,for example, an axial and/or radial and/or spherical curvature.

The transfer device has at least one focal length in response to the atleast one incident light beam propagating from the illumination sourceto the at least two optical sensors. As used herein, the term “focallength” of the transfer device refers to a distance over which incidentcollimated rays which may impinge the transfer device are brought into a“focus” which may also be denoted as “focal point”. Thus, the focallength constitutes a measure of an ability of the transfer device toconverge an impinging light beam. Thus, the transfer device may compriseone or more imaging elements which can have the effect of a converginglens. By way of example, the transfer device can have one or morelenses, in particular one or more refractive lenses, and/or one or moreconvex mirrors. In this example, the focal length may be defined as adistance from the center of the thin refractive lens to the principalfocal points of the thin lens. For a converging thin refractive lens,such as a convex or biconvex thin lens, the focal length may beconsidered as being positive and may provide the distance at which abeam of collimated light impinging the thin lens as the transfer devicemay be focused into a single spot. Additionally, the transfer device cancomprise at least one wavelength-selective element, for example at leastone optical filter. Additionally, the transfer device can be designed toimpress a predefined beam profile on the electromagnetic radiation, forexample, at the location of the sensor region and in particular thesensor area. The abovementioned optional embodiments of the transferdevice can, in principle, be realized individually or in any desiredcombination.

The transfer device has an optical axis. In particular, the receiverunit and the transfer device have a common optical axis. As used herein,the term “optical axis of the transfer device” generally refers to anaxis of mirror symmetry or rotational symmetry of the lens or lenssystem. The optical axis of the receiver unit may be a line of symmetryof the optical setup of the receiver unit. The transfer device, as anexample, may comprise at least one beam path, with the elements of thetransfer device in the beam path being located in a rotationallysymmetrical fashion with respect to the optical axis. Still, one or moreoptical elements located within the beam path may also be off-centeredor tilted with respect to the optical axis. In this case, however, theoptical axis may be defined sequentially, such as by interconnecting thecenters of the optical elements in the beam path, e.g. byinterconnecting the centers of the lenses, wherein, in this context, theoptical sensors are not counted as optical elements. The optical axisgenerally may denote the beam path. Therein, the receiver unit may havea single beam path along which a light beam may travel from the senderunit to the optical sensors, or may have a plurality of beam paths. Asan example, a single beam path may be given or the beam path may besplit into two or more partial beam paths. In the latter case, eachpartial beam path may have its own optical axis and the condition notedabove generally may refer to each beam path independently. The opticalsensors may be located in one and the same beam path or partial beampath. Alternatively, however, the optical sensors may also be located indifferent partial beam paths. In case the optical sensors aredistributed over different partial beam paths, at least one firstoptical sensor is located in at least one first partial beam path, beingoffset from the optical axis of the first partial beam path by a firstspatial offset, and at least one second optical sensor is located in atleast one second partial beam path, being offset from the optical axisof the second partial beam path by at least one second spatial offset,wherein the first spatial offset and the second spatial offset aredifferent.

The transfer device may constitute a coordinate system, wherein alongitudinal coordinate I is a coordinate along the optical axis andwherein d is a spatial offset from the optical axis. The coordinatesystem may be a polar coordinate system in which the optical axis of thetransfer device forms a z-axis and in which a distance from the z-axisand a polar angle may be used as additional coordinates. A directionparallel or antiparallel to the z-axis may be considered a longitudinaldirection, and a coordinate along the z-axis may be considered alongitudinal coordinate I. Any direction perpendicular to the z-axis maybe considered a transversal direction, and the polar coordinate and/orthe polar angle may be considered a transversal coordinate.

The optical sensors may be positioned off focus. As used herein, theterm “focus” generally refers to one or both of a minimum extend of acircle of confusion of the light beam caused by the transfer device or afocal length of the transfer device. As used herein, the term “circle ofconfusion” refers to a light spot caused by a cone of light rays of thelight beam focused by the transfer device. The circle of confusion maydepend on a focal length f of the transfer device, a longitudinaldistance from the sender unit to the transfer device, a diameter of anexit pupil of the transfer device, a longitudinal distance from thetransfer device to the light sensitive area, a distance from thetransfer device to an image of the sender unit. For example, forGaussian beams, a diameter of the circle of confusion may be a width ofthe Gaussian beam. In particular, for a point like object situated orplaced at infinite distance from the receiver unit the transfer devicemay be adapted to focus the light beam from the object into a focuspoint at the focal length of the transfer device. For non-point likeobjects situated or placed at infinite distance from the receiver unitthe transfer device may be adapted to focus the light beam from at leastone point of the object into a focus plane at the focal length of thetransfer device. For point like objects not situated or placed atinfinite distance from the receiver unit, the circle of confusion mayhave a minimum extend at least at one longitudinal coordinate. Fornon-point like objects not situated or placed at infinite distance fromthe receiver unit, the circle of confusion of the light beam from atleast one point of the object may have a minimum extend at least at onelongitudinal coordinate. As used herein, the term “positioned off focus”generally refers to a position other than the minimum extent of a circleof confusion of the light beam caused by the transfer device or a focallength of the transfer device. In particular, the focal point or minimumextend of the circle of confusion may be at a longitudinal coordinateI_(focus), whereas the position of each of the optical sensors may havea longitudinal coordinate I_(sensor) different from I_(focus). Forexample, the longitudinal coordinate I_(sensor) may be, in alongitudinal direction, arranged closer to the position of the transferdevice than the longitudinal coordinate I_(focus) or may be arrangedfurther away from the position of the transfer device than thelongitudinal coordinate I_(focus). Thus, the longitudinal coordinateI_(sensor) and the longitudinal coordinate I_(focus) may be situated atdifferent distances from the transfer device. For example, the opticalsensors may be spaced apart from the minimum extend of the circle ofconfusion in longitudinal direction by ±2% of focal length, preferablyby ±10% of focal length, most preferably ±20% of focal length. Forexample, at a focal length of the transfer device may be 20 mm and thelongitudinal coordinate I_(sensor) may be 19.5 mm, i.e. the sensors maybe positioned at 97.5% focal length, such that I_(sensor) is spacedapart from the focus by 2.5% of focal length.

The optical sensors are arranged such that the light-sensitive areas ofthe optical sensors differ in at least one of: their longitudinalcoordinate, their spatial offset, or their surface areas. Eachlight-sensitive area may have a geometrical center. As used herein, theterm “geometrical center” of an area generally may refer to a center ofgravity of the area. As an example, if an arbitrary point inside oroutside the area is chosen, and if an integral is formed over thevectors interconnecting this arbitrary point with each and every pointof the area, the integral is a function of the position of the arbitrarypoint. When the arbitrary point is located in the geometrical center ofthe area, the integral of the absolute value of the integral isminimized. Thus, in other words, the geometrical center may be a pointinside or outside the area with a minimum overall or sum distance fromall points of the area.

For example, each geometrical center of each light-sensitive area may bearranged at a longitudinal coordinate I_(center,i), wherein i denotesthe number of the respective optical sensor. In the case of the receiverunit comprising precisely two optical sensors and in the case of thedevice for optically surveilling comprising more than two opticalsensors, the optical sensors may comprise at least one first opticalsensor, wherein the first optical sensor, in particular the geometricalcenter, being arranged at a first longitudinal coordinate I_(center,1),and at least one second optical sensor, wherein the second opticalsensor, in particular the geometrical center, being at a secondlongitudinal coordinate I_(center,2), wherein the first longitudinalcoordinate and the second longitudinal coordinate differ. For example,the first optical sensor and the second optical sensor may be located indifferent planes which are offset in a direction of the optical axis.The first optical sensor may be arranged in front of the second opticalsensor. Thus, as an example, the first optical sensor may simply beplaced on the surface of the second optical sensor. Additionally oralternatively, the first optical sensor may be spaced apart from thesecond optical sensor, for example, by no more than five times thesquare root of a surface area of the first light-sensitive area.Additionally or alternatively, the first optical sensor may be arrangedin front of the second optical sensor and may be spaced apart from thesecond optical sensor by no more than 50 mm, preferably by no more than15 mm. Relative distance of the first optical sensor and second opticalsensor may depend, for example, on focal length or object distance.

The longitudinal coordinates of the optical sensors may also beidentical, as long as one of the above-mentioned conditions isfulfilled. For example, the longitudinal coordinates of the opticalsensors may be identical, but the light-sensitive areas may be spacedapart from the optical axis and/or the surface areas differ.

Each geometrical center of each light-sensitive area may be spaced apartfrom the optical axis of the transfer device, such as the optical axisof the beam path or the respective beam path in which the respectiveoptical sensor is located. The distance, in particular in transversaldirection, between the geometrical center and the optical axis isdenoted by the term “spatial offset”. In the case of precisely twooptical sensors and in the case of more than two optical sensors, theoptical sensors may comprise at least one first optical sensor beingspaced apart from the optical axis by a first spatial offset and atleast one second optical sensor being spaced apart from the optical axisby a second spatial offset, wherein the first spatial offset and thesecond spatial offset differ. The first and second spatial offsets, asan example, may differ by at least a factor of 1.2, more preferably byat least a factor of 1.5, more preferably by at least a factor of two.The spatial offsets may also be zero or may assume negative values, aslong as one of the above-mentioned conditions is fulfilled.

As used herein, the term “surface area” generally refers to both of ashape and a content of at least one light-sensitive area. In the case ofprecisely two optical sensors and in the case of more than two opticalsensors, the optical sensors may comprise at least one first opticalsensor having a first surface area and at least one second opticalsensor having a second surface area. In the case of the receiver unitcomprising more than two optical sensors, e.g. a sensor elementcomprising a matrix of optical sensors, a first group of optical sensorsor at least one of the optical sensors of the matrix may form a firstsurface area, wherein a second group of optical sensors or at least oneother optical sensor of the matrix may form a second surface area. Thefirst surface area and the second surface area may differ. Inparticular, the first surface area and the second surface area are notcongruent. Thus, the surface area of the first optical sensor and thesecond optical sensor may differ in one or more of the shape or content.For example, the first surface area may be smaller than the secondsurface area. As an example, both the first surface area and the secondsurface area may have the shape of a square or of a rectangle, whereinside lengths of the square or rectangle of the first surface area aresmaller than corresponding side lengths of the square or rectangle ofthe second surface area. Alternatively, as an example, both the firstsurface area and the second surface area may have the shape of a circle,wherein a diameter of the first surface area is smaller than a diameterof the second surface area. Again, alternatively, as an example, thefirst surface area may have a first equivalent diameter, and the secondsurface area may have a second equivalent diameter, wherein the firstequivalent diameter is smaller than the second equivalent diameter. Thesurface areas may be congruent, as long as one of the above-mentionedconditions is fulfilled.

The optical sensors, in particular the light-sensitive areas, mayoverlap or may be arranged such that no overlap between the opticalsensors is given.

As further used herein, the term “evaluation device” generally refers toan arbitrary device adapted to perform the named operations, preferablyby using at least one data processing device and, more preferably, byusing at least one processor and/or at least one application-specificintegrated circuit. Thus, as an example, the at least one evaluationdevice may comprise at least one data processing device having asoftware code stored thereon comprising a number of computer commands.The evaluation device may provide one or more hardware elements forperforming one or more of the named operations and/or may provide one ormore processors with software running thereon for performing one or moreof the named operations.

The evaluation device may be configured for generating the output basedon the distance by photon ratio (DPR) technique which is described e.g.in WO 2018/091649 A1, WO 2018/091638 A1 and WO 2018/091640, the contentof which is included by reference. The DPR technique allows distancemeasurements such as determining a longitudinal coordinate of the senderunit. In addition, the DPR technique also allows recognizing geometricalchanges to the light beam upon traversing the area of surveillance suchas partial coverage of the light beam.

The evaluation device is configured for generating an output bymonitoring at least one change of, firstly, the beam profile of the atleast one light beam upon traversing the at least one area ofsurveillance by evaluating the sensor signals and, further, of at leastone component of a location of the sender unit, wherein the component isdetermined with respect to the coordinate system of the transfer device,by evaluating a combined signal Q from the sensor signals. As usedherein, the term “combined signal Q” refers to a signal which isgenerated by combining the sensor signals, in particular by one or moreof dividing the sensor signals, dividing multiples of the sensor signalsor dividing linear combinations of the sensor signals. In particular,the combined signal may be a quotient signal. The combined signal Q maybe determined by using various means. As an example, a software meansfor deriving the combined signal, a hardware means for deriving thecombined signal, or both, may be used and may be implemented in theevaluation device. Thus, the evaluation device, as an example, maycomprise at least one divider, wherein the divider is configured forderiving the quotient signal. The divider may fully or partially beembodied as one or both of a software divider or a hardware divider.

The combined signal Q can be used for determining manipulations such aswillful and/or not intentional manipulations. The term “manipulation”refers to an arbitrary willful and/or not intentional intervention intothe device for optically surveillance resulting in a change of oneproperty of the light beam such as a change of a length and/or directionof the beam path. The beam path from the sender unit to the receiverunit may change due to changes in the optical system such as due to oneor more of water, scratches, introducing additional reflective elements,dirt, or even falseful arrangement of the components of the lightbarrier. The light barrier may also determine presence or absence of thereceiver unit, the sender unit or the reflective target. Specifically,such changes may lead to a change in one or more of x-, y-, orz-position of the sender unit, the beam profile, the combined signal Qand the sensor signals of the optical sensors. Changes of a length ofthe beam path may be detectable by monitoring the combined signal Q,specifically changes of the combined signal Q. The combined signal Q canbe used for determining a z-position of the sender unit. As the combinedsignal Q depends on the beam profile of the light beam, the combinedsignal Q can be used for determining changes in the beam profile. Theevaluation device may be configured to determine changes in the lengthof the beam path by determining and evaluating the combined signal Q asdescribed e.g. in WO 2018/091649 A1, WO 2018/091638 A1 and WO2018/091640 A1. The evaluation device may be configured for monitoringthe combined signal Q and for determining changes of the combined signalQ. The evaluation device may be configured for determining amanipulation based the determined change. For example, the evaluationdevice may be adapted for determining the longitudinal coordinate of thesender unit by evaluating the combined signal Q. In case the z-positionof the sender unit was changed, e.g. by introducing additionalreflective elements, the evaluation of the combined signal Q will resultin a longitudinal coordinate which is different from a referencelongitudinal coordinate. The evaluation device may be configured forcomparing the reference longitudinal coordinate and the measuredlongitudinal coordinate. The evaluation device may be configured forindicating a manipulation if the reference longitudinal coordinate andthe measured longitudinal coordinate differ, wherein differences withina tolerance range may be tolerated. Manipulations further may result ina change of the x- and/or y-position of the light beam impinges on therespective optical sensor and, thus, to changes of coverage, such as apartial coverage, of the light sensitive area of the respective opticalsensor. The combined signal Q can be used for detecting thesegeometrical changes of the light beam. Specifically, the evaluationdevice may be configured for determining a change of the at least onetransversal coordinate x and/or y of the sender unit by detectinggeometrical changes of the light beam, such as by monitoringsimultaneously the position of the center of gravity of the light spotand the total intensity of the light spot, whereas a change in in atleast one transversal coordinate x and/or y is likely in case the centerof gravity position changes, while the total intensity of the light spotis unchanged. A combination of monitoring several parameters such asmonitoring of the z-position in combination with monitoring the x-and/or y-position may allow enhancing reliability of the light barrier.

As used herein, the term “output” refers to an arbitrary indicationabout a change of a monitored parameter such as the beam profile of thelight beam upon traversing the at least one area and/or of the at leastone component of the location of the sender unit. The output may beand/or may comprise at least one output signal. The output may compriseat least one binary signal indicating whether or not a change ispresent. The output may comprise at least one information about thechange such as an amount of difference, which parameter is changed,which parameter were monitored or the like.

The evaluation device may further be designed for generating the atleast one output by monitoring a change of the sensor signals of theoptical sensors. As used herein, the term “at least one component of thelocation of the sender unit” refers to one or more of x-position,y-position and z-position of the sender unit. Specifically the term“position of the sender unit” refers to position of at least oneaperture of the sender unit. The evaluation device may be designed forgenerating the output by using at least one reference beam profile forthe at least one light beam generated by the illumination source and atleast one reference component for the at least one component of thelocation of the sender unit. As used herein, the term “change” refers todeviation such as from at least one reference beam profile and/or fromat least one reference position of the sender unit and/or from referencesensor signals and/or from a reference combined signal. In addition, theterm “change” refers to drop or even an absence such as from aninterruption of the light beam. One or more reference parameter selectedfrom the group consisting of the reference beam profile, the referencecomponent of location, the reference sensor signals, the referencecombined signal Q may be pre-determined and/or pre-defined. The at leastone reference beam profile and/or the at least one reference componentof the location of the sender unit and/or the reference sensor signalsand/or the reference combined signal Q may be stored during a teachingphase. The evaluation device may comprise at least one storage unit inwhich one or more of the reference beam profile, the reference componentof location, the reference sensor signals, the reference combined signalQ may be stored such as in a table or lookup table.

The evaluation device may be configured to compare the monitoredparameter with the respective reference parameter. A change may bedetermined by using at least one mathematical operation such assubtracting the respective reference value or profile from thedetermined value or profile or vice versa, respectively. The evaluationdevice may be configured to determine if the difference between thereference parameter and the monitored parameter exceeds at least onethreshold value and in case the difference exceeds the threshold toindicate a change. Manipulations may be defined as changes in one ormore of x-, y-, or z-position, the combined signal Q and the sensorsignals of the optical sensors, specifically, if the change concerns oneoptical sensor while the other sensor signal remains unchanged.

The combination of several surveillance parameters such as beam profile,combined signal Q, sensor signals, at least one component of locationmay allow providing a light barrier with enhanced reliability againstmanipulations. Specifically, the light barrier may be more reliableagainst reflections from highly reflective environment such as metalsheets or surfaces. Information from the beam profile or the x-yposition may be used for safety monitoring functions. As an example,changes of the beam profile may also indicate dirt on the optical systemthat may cause a failure of the safety function. Further, exhaust gases,steam, or particle emissions that may cause a failure of the system mayalso be detected by monitoring the beam profile. Monitoring thez-positions such as the longitudinal coordinate of the sender unit mayalso allow recognizing a shortening of the distance the light issupposed to have traveled. This may indicate a change in the opticalsystem such as due to water, scratches, manipulations, or dirt, or itmay indicate a falseful reassembly of the light barrier.

The evaluation device may be configured for initiating at least oneaction based on the output, wherein the at least one action is selectedfrom at least one of: providing at least one information such as asafety function, generating at least one warning, inducing at least oneinstruction, changing an output signal. The generating the warning maycomprise generating and/or changing at least one electronic signal.Specifically, the evaluation device actuates at least one safetyfunction based on the output. The information may be a warning, asafe-shutdown, an emergency warning, a violation information or thelike. The evaluation device may be configured for assigning theinformation to a time of event and for storing a combination of theinformation with the time of event in an information log. The warningmay comprise a visual, an audible or a haptic warning signal. Theinstruction may comprise initiating a shutdown of at least oneapparatus, such as of a machine. The evaluation device may be configuredthat not every change in one of the monitored parameters may lead to ashutdown or warning, but may lead in each case to an information aboutthe origin of the change such as the changed parameter.

The device for optically surveilling may comprise a plurality of senderunits and/or receiver units. The receiver units may be configured todetect the light beams having traversed the area of surveillance of morethan one sender unit simultaneously or non-simultaneously. To ensuresafe operation, the receiver unit may be configured to monitor thepresence of the light beam and/or the beam profile and/or at least oneof x-position, y-position, z-position of each sender unit and send outan information in case of a change. In case of a plurality of receiverunits the evaluation device may be configured to evaluate the sensorsignals of each of the receiver units using for example a multiplexingscheme. Additionally or alternatively, each of the receiver units maycomprise at least one evaluation device.

The evaluation device may comprise at least one safety unit comprisingat least one electrosensitive protective equipment (ESPE). The ESPE maycomprise a plurality of elements which are configured for protectivetripping and/or presence sensing purposes such as a sensing functionand/or a control or monitoring function. Specifically, the ESPE maycomprise at least one output signal switching device (OSSD). The OSSDmay be connected to a machine control system of an apparatus. In casethe evaluation device has actuated the safety function, specifically hasinitiated the action as described above, the machine control systemresponds by going into a safe state such as an OFF state. The apparatusmay comprise one or more of at least one electrically powered machineprimary control element (MPCE) configured for controlling normaloperation of the apparatus, at least one machine secondary controlelement (MSCE) which is a further machine control element configured forremoving power source from prime mover of hazardous parts, at least onefinal switching device (FSD), at least one secondary switching device(SSD), normally closed (NC) contacts and normally open (NO) contacts.The FSD may be configured in response to the indication from the OSSD tointerrupt the circuit connecting the machine control system to themachine primary control system. In this situation, the SSD may beconfigured for performing a back-up function by going to the OFF stateand initiating further machine control actions such as de-energizing theMSCE.

The evaluation device may comprise at least one safe digital inputchannel and/or at least one safe digital output channel and/or at leastone diagnostics channel, such as an IO-Link based diagnostics channel.The evaluation device may be connected to a further device such as acomputer, laptop, console device, or mobile device for the teaching,parameter setup, setup, or for diagnostics, or the like. The evaluationdevice may comprise a memory for storing information such as diagnosticsinformation to be transmitted immediately or at a later time to afurther device, such as to one of the aforementioned further devices.The evaluation device may comprise an M12 connector for connecting tofurther devices or for connecting sender and receiver unit. Theevaluation device may detect ambient incident light using the opticalsensor or a further optical sensor. The ambient incident light level maybe transmitted to a further device such as for diagnostics. Theevaluation device may output errors and possible countermeasures relatedto the errors.

The sender and/or receiver unit may comprise at least one indicatorillumination source, such as an indicator LED indicating a status of thesender and/or receiver unit or the type of an incident by changing acolor of the illumination and/or by using different blinking ormodulation patterns. As an example, different error levels may beindicated by a continuous or blinking red LED light, whereas theblinking may occur at frequencies of 1-10 Hz. Orange or greenillumination may be used to indicate whether a stable amount of light isreceived by the receiver unit.

The evaluation device may be adapted to generate different signals orinformation depending on the area of surveillance such as by dividingthe area of surveillance in at least two subareas, wherein the type ofinformation that is generated is dependent on the subarea. For example,when the light beam is interrupted in a first subarea, a warning signalis generated, whereas when the light beam is interrupted in a secondsubarea, a shutdown signal is generated. This may allow to definedifferent safety zones.

Using the DPR technique may be advantageous since it is possible to usecommonplace and cheap Si-sensors such as bi-cells or quadrant diodesthat are much faster and have a larger bandwidth than for example FiPsensors. Further Si-sensors may be more homogeneous and entirelyintensity independent, whereas in FiP devices homogeneity requirementscan make fabrication costly and intensity independence of the FiPquotient requires additional technical effort. For possible embodimentsof sensors using DPR technique reference is made to WO 2018/091649 A1,WO 2018/091638 A1 and WO 2018/091640 A1, the content of which isincluded by reference. In the following the DPR technique for exemplarysensor setups is described, specifically the determination of thecombined signal Q and determining the longitudinal coordinate z of thesender unit from the combined signal Q is described.

The evaluation device may be configured for deriving the combined signalQ by one or more of dividing the sensor signals, dividing multiples ofthe sensor signals, dividing linear combinations of the sensor signals.The evaluation device may be configured for using at least onepredetermined relationship between the combined signal Q and thelongitudinal coordinate for determining the longitudinal coordinate. Thedetermining of the at least one longitudinal coordinate of the senderunit may be performed by the at least one evaluation device. Thus, as anexample, the relationship may be implemented in software and/orhardware, such as by implementing one or more lookup tables. Thus, as anexample, the evaluation device may comprise one or more programmabledevices such as one or more computers, application-specific integratedcircuits (ASICs), Digital Signal Processors (DSPs), or FieldProgrammable Gate Arrays (FPGAs) which are configured to perform theabove-mentioned evaluation, in order to determine the at least onelongitudinal coordinate of the sender unit. Additionally oralternatively, however, the evaluation device may also fully orpartially be embodied by hardware.

For example, the evaluation device is configured for deriving thecombined signal Q by

${Q\left( z_{O} \right)} = \frac{\underset{A_{1}}{\int\int}{E\left( {x,{y;z_{O}}} \right)}{dxdy}}{\underset{A_{2}}{\int\int}{E\left( {x,y,z_{O}} \right)}{dxdy}}$

-   -   wherein x and y are transversal coordinates, A1 and A2 are areas        of the beam profile of the light beam at the position of the        optical sensors, and E(x,y,z_(o)) denotes the beam profile for        the distance of the sender unit z_(o). Area A1 and area A2 may        differ. In particular, A1 and A2 are not congruent. Thus, A1 and        A2 may differ in one or more of the shape or content. The beam        profile may be a cross section of the light beam. The beam        profile may be selected from the group consisting of a trapezoid        beam profile; a triangle beam profile; a conical beam profile        and a linear combination of Gaussian beam profiles. Generally        the beam profile is dependent on luminance L(z_(o)) and beam        shape S(x,y;z_(o)), E(x,y;zo)=L·S. Thus, by deriving the        combined signal it may allow determining the longitudinal        coordinate independent from luminance.

Each of the sensor signals may comprise at least one information of atleast one area of the beam profile of the light beam. As used herein,the term “area of the beam profile” generally refers to an arbitraryregion of the beam profile at the sensor position used for determiningthe combined signal Q. The light-sensitive areas may be arranged suchthat a first sensor signal comprises information of a first area of thebeam profile and a second sensor signal comprises information of asecond area of the beam profile. The first area of the beam profile andsecond area of the beam profile may be one or both of adjacent oroverlapping regions. The first area of the beam profile and the secondarea of the beam profile may be not congruent in area.

The evaluation device may be configured to determine and/or to selectthe first area of the beam profile and the second area of the beamprofile. The first area of the beam profile may comprise essentiallyedge information of the beam profile and the second area of the beamprofile may comprise essentially center information of the beam profile.The beam profile may have a center, i.e. a maximum value of the beamprofile and/or a center point of a plateau of the beam profile and/or ageometrical center of the light spot, and falling edges extending fromthe center. The second region may comprise inner regions of the crosssection and the first region may comprise outer regions of the crosssection. As used herein, the term “essentially center information”generally refers to a low proportion of edge information, i.e.proportion of the intensity distribution corresponding to edges,compared to a proportion of the center information, i.e. proportion ofthe intensity distribution corresponding to the center. Preferably thecenter information has a proportion of edge information of less than10%, more preferably of less than 5%, most preferably the centerinformation comprises no edge content. As used herein, the term“essentially edge information” generally refers to a low proportion ofcenter information compared to a proportion of the edge information. Theedge information may comprise information of the whole beam profile, inparticular from center and edge regions. The edge information may have aproportion of center information of less than 10%, preferably of lessthan 5%, more preferably the edge information comprises no centercontent. At least one area of the beam profile may be determined and/orselected as second area of the beam profile if it is close or around thecenter and comprises essentially center information. At least one areaof the beam profile may be determined and/or selected as first area ofthe beam profile if it comprises at least parts of the falling edges ofthe cross section. For example, the whole area of the cross section maybe determined as first region. The first area of the beam profile may bearea A2 and the second area of the beam profile may be area A1.

The edge information may comprise information relating to a number ofphotons in the first area of the beam profile and the center informationmay comprise information relating to a number of photons in the secondarea of the beam profile. The evaluation device may be adapted fordetermining an area integral of the beam profile. The evaluation devicemay be adapted to determine the edge information by integrating and/orsumming of the first area. The evaluation device may be adapted todetermine the center information by integrating and/or summing of thesecond area. For example, the beam profile may be a trapezoid beamprofile and the evaluation device may be adapted to determine anintegral of the trapezoid. Further, when trapezoid beam profiles may beassumed, the determination of edge and center signals may be replaced byequivalent evaluations making use of properties of the trapezoid beamprofile such as determination of the slope and position of the edges andof the height of the central plateau and deriving edge and centersignals by geometric considerations.

Additionally or alternatively, the evaluation device may be adapted todetermine one or both of center information or edge information from atleast one slice or cut of the light spot. This may be realized, forexample, by replacing the area integrals in the combined signal Q byline integrals along the slice or cut. For improved accuracy, severalslices or cuts through the light spot may be used and averaged. In caseof an elliptical spot profile, averaging over several slices or cuts mayresult in an improved distance information.

The evaluation device may be configured to derive the combined signal Qby one or more of dividing the edge information and the centerinformation, dividing multiples of the edge information and the centerinformation, dividing linear combinations of the edge information andthe center information. Thus, essentially, photon ratios may be used asthe physical basis of the method.

The two of the optical sensors may be designed and arranged as follows

-   -   at least one first optical sensor having a first light-sensitive        area, wherein the first optical sensor is configured to generate        at least one first sensor signal in response to an illumination        of the first light-sensitive area by the light beam propagating        from the sender unit to the receiver unit; and    -   at least one second optical sensor having a second        light-sensitive area, wherein the second optical sensor is        configured to generate at least one second sensor signal in        response to an illumination of the second light-sensitive area        by the light beam, wherein the first light-sensitive area is        smaller than the second light-sensitive area.

The evaluation device may be configured for generating the output byevaluating the first and second sensor signals. The evaluation devicemay be further designed for generating the at least one output bymonitoring a change of the first sensor signal or of the second sensorsignal.

In this embodiment the optical sensors may be arranged such that thelight-sensitive areas of the optical sensors differ in theirlongitudinal coordinate and/or their surface areas. The evaluationdevice is further designed for generating the at least one output bymonitoring a change of the first sensor signal or of the second sensorsignal. For one-way light barriers, the first and second light-sensitiveareas specifically may be oriented towards the sender unit.Alternatively, for reflective light barriers, the sender unit and thefirst and the second light-sensitive areas may be oriented towards areflective target.

The light beam propagating from the sender unit to the receiver unitspecifically may fully illuminate the first light-sensitive area, suchthat the first light-sensitive area is fully located within the lightbeam, with a width of the light beam being larger than thelight-sensitive area of the first optical sensor. Contrarily,preferably, the light beam propagating from the sender unit to thereceiver unit specifically may create a light spot on the secondlight-sensitive area, which is smaller than the second light-sensitivearea, such that the light spot is fully located within the secondlight-sensitive area. Within the light spot on the secondlight-sensitive area, a shadow created by the first optical sensor maybe located. Thus, generally, the first optical sensor, having thesmaller first light-sensitive area, may be located in front of thesecond optical sensor, as seen from the sender unit, with the firstlight-sensitive area being fully located within the light beam and withthe light beam generating a light spot on the second light-sensitivearea being smaller than the second light-sensitive area, and withfurther a shadow created by the first optical sensor within the lightspot. The situation may easily be adjusted by a person skilled in theart of optics by choosing one or more appropriate lenses or elementshaving a focusing or defocusing effect on the light beam, such as byusing an appropriate transfer device as will be outlined in furtherdetail below. As further used herein, a light spot generally refers to avisible or detectable round or non-round illumination of an article, anarea or object by a light beam.

As outlined above, the first light-sensitive area is smaller than thesecond light-sensitive area. As used therein, the term “is smaller than”refers to the fact that the surface area of the first light-sensitivearea is smaller than the surface area of the second light-sensitivearea, such as by at least a factor of 0.9, e.g. at least a factor of 0.7or even by at least a factor of 0.5. As an example, both the firstlight-sensitive area and the second light-sensitive area may have theshape of a square or of a rectangle, wherein side lengths of the squareor rectangle of the first light-sensitive area are smaller thancorresponding side lengths of the square or rectangle of the secondlight-sensitive area. Alternatively, as an example, both the firstlight-sensitive area and the second light-sensitive area may have theshape of a circle, wherein a diameter of the first light-sensitive areais smaller than a diameter of the second light-sensitive area. Again,alternatively, as an example, the first light-sensitive area may have afirst equivalent diameter, and the second light-sensitive area may havea second equivalent diameter, wherein the first equivalent diameter issmaller than the second equivalent diameter.

The first light-sensitive area specifically may overlap with the secondlight-sensitive area in a direction of propagation of the light beam.The light beam may illuminate both the first light-sensitive area and,fully or partially, the second light-sensitive area. Thus, as anexample, as seen from a point located on an optical axis of the receiverunit, the first light-sensitive area may be located in front of thesecond light-sensitive area, such that the first light-sensitive area,as seen from the sender unit, is fully located within the secondlight-sensitive area. When the light beam propagates towards the firstand second light-sensitive areas, as outlined above, the light beam mayfully illuminate the first light-sensitive area and may create a lightspot on the second light-sensitive area, wherein a shadow created by thefirst optical sensor is located within the light spot. It shall benoted, however, that other embodiments are feasible.

Specifically, the evaluation device may be configured to determine theat least one coordinate z of the sender unit by using at least oneknown, determinable or predetermined relationship between the combinedsignal derived from the first and second sensor signals and thelongitudinal coordinate. Thus, the evaluation device specifically may beconfigured for deriving the combined signal Q by dividing the first andsecond sensor signals, by dividing multiples of the first and secondsensor signals or by dividing linear combinations of the first andsecond sensor signals. As an example, Q may simply be determined asQ=s1/s2 or Q=s2/s1, with s1 denoting the first sensor signal and s2denoting the second sensor signal. Additionally or alternatively, Q maybe determined as Q=a·s1/b·s2 or Q=b·s2/a·s1, with a and b being realnumbers which, as an example, may be predetermined or determinable.Additionally or alternatively, Q may be determined asQ=(a·s1+b·s2)/(c·s1+d·s2), with a, b, c and d being real numbers which,as an example, may be predetermined or determinable. As a simple examplefor the latter, Q may be determined as Q=s1/(s1+s2). Other combinedsignals are feasible.

Typically, in the setup described above, Q is a monotonous function ofthe longitudinal coordinate of the sender unit and/or of the size of thelight spot such as the diameter or equivalent diameter of the lightspot. Thus, as an example, specifically in case linear optical sensorsare used, the quotient Q=s1/s2 is a monotonously decreasing function ofthe size of the light spot. Without wishing to be bound by this theory,it is believed that this is due to the fact that, in the preferred setupdescribed above, both the first signal s1 and the second signal s2decrease as a square function with increasing distance to the lightsource, since the amount of light reaching the receiver unit decreases.Therein, however, the first signal s1 decreases more rapidly than thesecond signal s2, since, in the optical setup as used in theexperiments, the light spot in the image plane grows and, thus, isspread over a larger area. The quotient of the first and second sensorsignals, thus, continuously decreases with increasing diameter of thelight beam or diameter of the light spot on the first and secondlight-sensitive areas. The quotient, further, is mainly independent fromthe total power of the light beam, since the total power of the lightbeam forms a factor both in the first sensor signal and in the secondsensor signal. Consequently, the combined signal Q may form a secondarysignal which provides a unique and unambiguous relationship between thefirst and second sensor signals and the size or diameter of the lightbeam. Since, on the other hand, the size or diameter of the light beamis dependent on a distance between the sender unit, from which the lightbeam propagates towards the receiver unit, and the receiver unit itself,i.e. dependent on the longitudinal coordinate of the sender unit, aunique and unambiguous relationship between the first and second sensorsignals and the longitudinal coordinate may exist. For the latter,reference e.g. may be made to WO 2014/097181 A1. The predeterminedrelationship may be determined by analytical considerations, such as byassuming a linear combination of Gaussian light beams, by empiricalmeasurements, such as measurements measuring the first and second sensorsignals or a secondary signal derived thereof as a function of thelongitudinal coordinate of the sender unit, or both. The evaluationdevice may be configured for determining the longitudinal coordinate byevaluating the combined signal Q. The evaluation device may beconfigured for using at least one predetermined relationship between thecombined signal Q and the longitudinal coordinate. The predeterminedrelationship may be one or more of an empiric relationship, asemi-empiric relationship and an analytically derived relationship. Theevaluation device may comprise at least one data storage device forstoring the predetermined relationship, such as a lookup list or alookup table.

The first and second optical sensors specifically may be arrangedlinearly in one and the same beam path of the receiver unit. As usedherein, the term “linearly” generally refers to that the sensors arearranged along one axis. Thus, as an example, the first and secondoptical sensors both may be located on an optical axis of the receiverunit. Specifically, the first and second optical sensors may be arrangedconcentrically with respect to an optical axis. The first optical sensormay be arranged in front of the second optical sensor. Thus, as anexample, the first optical sensor may simply be placed on the surface ofthe second optical sensor. Additionally or alternatively, the firstoptical sensor may be spaced apart from the second optical sensor by nomore than five times the square root of a surface area of the firstlight-sensitive area. Additionally or alternatively, the first opticalsensor may be arranged in front of the second optical sensor and may bespaced apart from the second optical sensor by no more than 50 mm,preferably by no more than 15 mm.

As outlined above, the second light-sensitive area is larger than thefirst light-sensitive area. Thus, as an example, the secondlight-sensitive area may be larger by at least a factor of two, morepreferably by at least a factor of three and most preferably by at leasta factor of five and the first light-sensitive area. The firstlight-sensitive area specifically may be a small light-sensitive area,such that, preferably, the light beam fully illuminates thislight-sensitive area. Thus, as an example which may be applicable totypical optical configurations, the first light-sensitive area may havea surface area of 0.01 mm² to 150 mm², more preferably a surface area of0.1 mm² to 100 mm². The second light-sensitive area specifically may bea large area. Thus, preferably, within a measurement range of thereceiver unit, light spots generated by a light beam propagating fromthe sender unit of the receiver may fully be located within the secondlight-sensitive area, such that the light spot is fully located withinthe borders of the second light-sensitive area. As an example, which isapplicable e.g. in typical optical setups, the second light-sensitivearea may have a surface area of 1 mm² to 1000 mm², more preferably asurface area of 2 mm² to 600 mm².

The first and second optical sensors each, independently, may be opaque,transparent or semitransparent. For the sake of simplicity, however,opaque sensors which are not transparent for the light beam, may beused, since these opaque sensors generally are widely commerciallyavailable.

The first and second optical sensors each specifically may be uniformsensors having a single light-sensitive area each. Thus, the first andsecond optical sensors specifically may be non-pixelated opticalsensors.

As outlined above, by evaluating the first and second sensor signals,the evaluation device may be enabled to determine the at least onelongitudinal coordinate of the sender unit. In addition, however, othercoordinates of the sender unit, including one or more transversalcoordinates and/or rotational coordinates, may be determined by theevaluation device. Thus, as an example, one or more additionaltransversal sensors may be used for determining at least one transversalcoordinate. Various transversal sensors are generally known in the art,such as the transversal sensors disclosed in WO 2014/097181 A1 and/orother position-sensitive devices (PSDs), such as quadrant diodes, CCD orCMOS chips or the like. These devices may generally also be implementedinto the receiver unit. As an example, a part of the light beam may besplit off within the receiver unit, by at least one beam splittingelement. The split-off portion, as an example, may be guided towards atransversal sensor, such as a CCD or CMOS chip or a camera sensor, and atransversal position of a light spot generated by the split-off portionon the transversal sensor may be determined, thereby determining atleast one transversal coordinate.

Other embodiments of the first optical sensor and the second opticalsensor, however, are feasible. For example, the first optical sensor andthe second optical sensor may have light-sensitive areas having anidentical size. In this case, for example, the first light-sensitivearea and the second light sensitive area may be arranged such that thelight-sensitive areas differ in their longitudinal coordinate.

In a further embodiment of the present invention, the receiver unit maycomprise at least one sensor element having a matrix of optical sensors,the optical sensors each having a light-sensitive area. Each opticalsensor may be configured to generate at least one sensor signal inresponse to an illumination of the light-sensitive area by the lightbeam propagating from the sender unit to the receiver unit. In thisembodiment the optical sensors may be arranged such that thelight-sensitive areas of the optical sensors differ in spatial offsetand/or surface areas. The evaluation device may be configured forevaluating the sensor signals, by

-   -   a) determining at least one optical sensor having the highest        sensor signal and forming at least one center signal;    -   b) evaluating the sensor signals of the optical sensors of the        matrix and forming at least one sum signal;    -   c) determining at least one combined signal by combining the        center signal and the sum signal; and    -   d) determining at least one longitudinal coordinate z of the        sender unit by evaluating the combined signal.

As used herein, the term “sensor element” generally refers to a deviceor a combination of a plurality of devices configured for sensing atleast one parameter. In the present case, the parameter specifically maybe an optical parameter, and the sensor element specifically may be anoptical sensor element. The sensor element may be formed as a unitary,single device or as a combination of several devices. As further usedherein, the term “matrix” generally refers to an arrangement of aplurality of elements in a predetermined geometrical order. The matrix,as will be outlined in further detail below, specifically may be or maycomprise a rectangular matrix having one or more rows and one or morecolumns. The rows and columns specifically may be arranged in arectangular fashion. It shall be outlined, however, that otherarrangements are feasible, such as nonrectangular arrangements. As anexample, circular arrangements are also feasible, wherein the elementsare arranged in concentric circles or ellipses about a center point. Forexample, the matrix may be a single row of pixels. Other arrangementsare feasible.

The optical sensors of the matrix specifically may be equal in one ormore of size, sensitivity and other optical, electrical and mechanicalproperties. The light-sensitive areas of all optical sensors of thematrix specifically may be located in a common plane, the common planepreferably facing the sender unit, such that the light beam propagatingfrom the sender unit to the receiver unit may generate a light spot onthe common plane. As explained in more detail in one or more of theabove-mentioned prior art documents, e.g. in WO 2012/110924 A1 or WO2014/097181 A1, typically, a predetermined or determinable relationshipexists between a size of a light spot, such as a diameter of the lightspot, a beam waist or an equivalent diameter, and the longitudinalcoordinate of the sender unit from which the light beam propagatestowards the receiver unit. Without wishing to be bound by this theory,the light spot, may be characterized by two measurement variables: ameasurement signal measured in a small measurement patch in the centeror close to the center of the light spot, also referred to as the centersignal, and an integral or sum signal integrated over the light spot,with or without the center signal. For a light beam having a certaintotal power which does not change when the beam is widened or focused,the sum signal should be independent from the spot size of the lightspot, and, thus, should, at least when linear optical sensors withintheir respective measurement range are used, be independent from thedistance between the sender unit and the receiver unit. The centersignal, however, is dependent on the spot size. Thus, the center signaltypically increases when the light beam is focused, and decreases whenthe light beam is defocused. By comparing the center signal and the sumsignal, thus, an item of information on the size of the light spotgenerated by the light beam and, thus, on the longitudinal coordinate ofthe sender unit may be generated. The comparing of the center signal andthe sum signal, as an example, may be done by forming the combinedsignal Q out of the center signal and the sum signal and by using apredetermined or determinable relationship between the longitudinalcoordinate and the combined signal for deriving the longitudinalcoordinate.

The use of a matrix of optical sensors provides a plurality ofadvantages and benefits. Thus, the center of the light spot generated bythe light beam on the sensor element, such as on the common plane of thelight-sensitive areas of the optical sensors of the matrix of the sensorelement, may vary with a transversal position of the sender unit. Byusing a matrix of optical sensors, the receiver unit may adapt to thesechanges in conditions and, thus, may determine the center of the lightspot simply by comparing the sensor signals. Consequently, the receiverunit may, by itself, choose the center signal and determine the sumsignal and, from these two signals, derive a combined signal whichcontains information on the longitudinal coordinate of the sender unit.By evaluating the combined signal, the longitudinal coordinate of thesender unit may, thus, be determined. The use of the matrix of opticalsensors, thus, provides a significant flexibility in terms of theposition of the sender unit, specifically in terms of a transversalposition of the sender unit.

The transversal position of the light spot on the matrix of opticalsensors, such as the transversal position of the at least one opticalsensor generating the sensor signal, may even be used as an additionalitem of information, from which at least one item of information on atransversal position of the sender unit may be derived, as e.g.disclosed in WO 2014/198629 A1. Additionally or alternatively, thereceiver unit may comprise at least one additional transversal detectorfor, in addition to the at least one longitudinal coordinate, detectingat least one transversal coordinate of the sender unit.

Consequently, in accordance with the present invention, the term “centersignal” generally refers to the at least one sensor signal comprisingessentially center information of the beam profile. As used herein, theterm “highest sensor signal” refers to one or both of a local maximum ora maximum in a region of interest. For example, the center signal may bethe signal of the at least one optical sensor having the highest sensorsignal out of the plurality of sensor signals generated by the opticalsensors of the entire matrix or of a region of interest within thematrix, wherein the region of interest may be predetermined ordeterminable within an image generated by the optical sensors of thematrix. The center signal may arise from a single optical sensor or, aswill be outlined in further detail below, from a group of opticalsensors, wherein, in the latter case, as an example, the sensor signalsof the group of optical sensors may be added up, integrated or averaged,in order to determine the center signal. The group of optical sensorsfrom which the center signal arises may be a group of neighboringoptical sensors, such as optical sensors having less than apredetermined distance from the actual optical sensor having the highestsensor signal, or may be a group of optical sensors generating sensorsignals being within a predetermined range from the highest sensorsignal. The group of optical sensors from which the center signal arisesmay be chosen as large as possible in order to allow maximum dynamicrange. The evaluation device may be adapted to determine the centersignal by integration of the plurality of sensor signals, for examplethe plurality of optical sensors around the optical sensor having thehighest sensor signal. For example, the beam profile may be a trapezoidbeam profile and the evaluation device may be adapted to determine anintegral of the trapezoid, in particular of a plateau of the trapezoid.

Similarly, the term “sum signal” generally refers to a signal comprisingessentially edge information of the beam profile. For example, the sumsignal may be derived by adding up the sensor signals, integrating overthe sensor signals or averaging over the sensor signals of the entirematrix or of a region of interest within the matrix, wherein the regionof interest may be predetermined or determinable within an imagegenerated by the optical sensors of the matrix. When adding up,integrating over or averaging over the sensor signals, the actualoptical sensors from which the sensor signal is generated may be leftout of the adding, integration or averaging or, alternatively, may beincluded into the adding, integration or averaging. The evaluationdevice may be adapted to determine the sum signal by integrating signalsof the entire matrix, or of the region of interest within the matrix.For example, the beam profile may be a trapezoid beam profile and theevaluation device may be adapted to determine an integral of the entiretrapezoid. Further, when trapezoid beam profiles may be assumed, thedetermination of edge and center signals may be replaced by equivalentevaluations making use of properties of the trapezoid beam profile suchas determination of the slope and position of the edges and of theheight of the central plateau and deriving edge and center signals bygeometric considerations.

Additionally or alternatively, the evaluation device may be adapted todetermine one or both of center information or edge information from atleast one slice or cut of the light spot. This may be realized forexample by replacing the area integrals in the combined signal Q by lineintegrals along the slice or cut. For improved accuracy, several slicesor cuts through the light spot may be used and averaged. In case of anelliptical spot profile, averaging over several slices or cuts mayresult in an improved distance information.

Similarly, the term “combined signal”, as used herein, generally refersto a signal which is generated by combining the center signal and thesum signal. Specifically, the combination may include one or more of:forming a quotient of the center signal and the sum signal or viceversa; forming a quotient of a multiple of the center signal and amultiple of the sum signal or vice versa; forming a quotient of a linearcombination of the center signal and a linear combination of the sumsignal or vice versa. Additionally or alternatively, the combined signalmay comprise an arbitrary signal or signal combination which contains atleast one item of information on a comparison between the center signaland the sum signal.

The light beam specifically may fully illuminate the at least oneoptical sensor from which the center signal is generated, such that theat least one optical sensor from which the center signal arises is fullylocated within the light beam, with a width of the light beam beinglarger than the light-sensitive area of the at least one optical sensorfrom which the sensor signal arises. Contrarily, preferably, the lightbeam specifically may create a light spot on the entire matrix which issmaller than the matrix, such that the light spot is fully locatedwithin the matrix. This situation may easily be adjusted by a personskilled in the art of optics by choosing one or more appropriate lensesor elements having a focusing or defocusing effect on the light beam,such as by using an appropriate transfer device.

As outlined above, the center signal generally may be a single sensorsignal, such as a sensor signal from the optical sensor in the center ofthe light spot, or may be a combination of a plurality of sensorsignals, such as a combination of sensor signals arising from opticalsensors in the center of the light spot, or a secondary sensor signalderived by processing a sensor signal derived by one or more of theaforementioned possibilities. The determination of the center signal maybe performed electronically, since a comparison of sensor signals isfairly simply implemented by conventional electronics, or may beperformed fully or partially by software. Specifically, the centersignal may be selected from the group consisting of: the highest sensorsignal; an average of a group of sensor signals being within apredetermined range of tolerance from the highest sensor signal; anaverage of sensor signals from a group of optical sensors containing theoptical sensor having the highest sensor signal and a predeterminedgroup of neighboring optical sensors; a sum of sensor signals from agroup of optical sensors containing the optical sensor having thehighest sensor signal and a predetermined group of neighboring opticalsensors; a sum of a group of sensor signals being within a predeterminedrange of tolerance from the highest sensor signal; an average of a groupof sensor signals being above a predetermined threshold; a sum of agroup of sensor signals being above a predetermined threshold; anintegral of sensor signals from a group of optical sensors containingthe optical sensor having the highest sensor signal and a predeterminedgroup of neighboring optical sensors; an integral of a group of sensorsignals being within a predetermined range of tolerance from the highestsensor signal; an integral of a group of sensor signals being above apredetermined threshold.

As outlined above, raw sensor signals of the optical sensors may be usedfor evaluation or secondary sensor signals derived thereof. As usedherein, the term “secondary sensor signal” generally refers to a signal,such as an electronic signal, more preferably an analogue and/or adigital signal, which is obtained by processing one or more raw signals,such as by filtering, averaging, demodulating or the like. Thus, imageprocessing algorithms may be used for generating secondary sensorsignals from the totality of sensor signals of the matrix or from aregion of interest within the matrix. Specifically, the evaluationdevice may be configured for transforming the sensor signals of theoptical sensor, thereby generating secondary optical sensor signals,wherein the evaluation device is configured for performing steps a)-d)by using the secondary optical sensor signals. The transformation of thesensor signals specifically may comprise at least one transformationselected from the group consisting of: a filtering; a selection of atleast one region of interest; a formation of a difference image betweenan image created by the sensor signals and at least one offset; aninversion of sensor signals by inverting an image created by the sensorsignals; a formation of a difference image between an image created bythe sensor signals at different times; a background correction; adecomposition into color channels; a decomposition into hue; saturation;and brightness channels; a frequency decomposition; a singular valuedecomposition; applying a Canny edge detector; applying a Laplacian ofGaussian filter; applying a Difference of Gaussian filter; applying aSobel operator; applying a Laplace operator; applying a Scharr operator;applying a Prewitt operator; applying a Roberts operator; applying aKirsch operator; applying a high-pass filter; applying a low-passfilter; applying a Fourier transformation; applying aRadon-transformation; applying a Hough-transformation; applying awavelet-transformation; a thresholding; creating a binary image. Theregion of interest may be determined manually by a user or maybedetermined automatically, such as by recognizing an object within animage generated by the optical sensors. As an example, a vehicle, aperson or another type of predetermined object may be determined byautomatic image recognition within an image, i.e. within the totality ofsensor signals generated by the optical sensors, and the region ofinterest may be chosen such that the object is located within the regionof interest. In this case, the evaluation, such as the determination ofthe longitudinal coordinate, may be performed for the region ofinterest, only. Other implementations, however, are feasible.

As outlined above, the detection of the center of the light spot, i.e.the detection of the center signal and/or of the at least one opticalsensor from which the center signal arises, may be performed fully orpartially electronically or fully or partially by using one or moresoftware algorithms. Specifically, the evaluation device may comprise atleast one center detector for detecting the at least one highest sensorsignal and/or for forming the center signal. The center detectorspecifically may fully or partially be embodied in software and/or mayfully or partially be embodied in hardware. The center detector mayfully or partially be integrated into the at least one sensor elementand/or may fully or partially be embodied independently from the sensorelement.

As outlined above, the sum signal may be derived from all sensor signalsof the matrix, from the sensor signals within a region of interest orfrom one of these possibilities with the sensor signals arising from theoptical sensors contributing to the center signal excluded. In everycase, a reliable sum signal may be generated which may be compared withthe center signal reliably, in order to determine the longitudinalcoordinate. Generally, the sum signal may be selected from the groupconsisting of: an average over all sensor signals of the matrix; a sumof all sensor signals of the matrix; an integral of all sensor signalsof the matrix; an average over all sensor signals of the matrix exceptfor sensor signals from those optical sensors contributing to the centersignal; a sum of all sensor signals of the matrix except for sensorsignals from those optical sensors contributing to the center signal; anintegral of all sensor signals of the matrix except for sensor signalsfrom those optical sensors contributing to the center signal; a sum ofsensor signals of optical sensors within a predetermined range from theoptical sensor having the highest sensor signal; an integral of sensorsignals of optical sensors within a predetermined range from the opticalsensor having the highest sensor signal; a sum of sensor signals above acertain threshold of optical sensors being located within apredetermined range from the optical sensor having the highest sensorsignal; an integral of sensor signals above a certain threshold ofoptical sensors being located within a predetermined range from theoptical sensor having the highest sensor signal. Other options, however,exist.

The summing may be performed fully or partially in software and/or maybe performed fully or partially in hardware. A summing is generallypossible by purely electronic means which, typically, may easily beimplemented into the receiver unit. Thus, in the art of electronics,summing devices are generally known for summing two or more electricalsignals, both analogue signals and digital signals. Thus, the evaluationdevice may comprise at least one summing device for forming the sumsignal. The summing device may fully or partially be integrated into thesensor element or may fully or partially be embodied independently fromthe sensor element. The summing device may fully or partially beembodied in one or both of hardware or software.

As outlined above, the comparison between the center signal and the sumsignal specifically may be performed by forming one or more quotientsignals. Thus, generally, the combined signal may be a quotient signal,derived by one or more of: forming a quotient of the center signal andthe sum signal or vice versa; forming a quotient of a multiple of thecenter signal and a multiple of the sum signal or vice versa; forming aquotient of a linear combination of the center signal and a linearcombination of the sum signal or vice versa; forming a quotient of thecenter signal and a linear combination of the sum signal and the centersignal or vice versa; forming a quotient of the sum signal and a linearcombination of the sum signal and the center signal or vice versa;forming a quotient of an exponentiation of the center signal and anexponentiation of the sum signal or vice versa. Other options, however,exist. The evaluation device may be configured for forming the one ormore quotient signals. The evaluation device may further be configuredfor determining the at least one longitudinal coordinate by evaluatingthe at least one quotient signal.

The evaluation device specifically may be configured for using at leastone predetermined relationship between the combined signal Q and thelongitudinal coordinate, in order to determine the at least onelongitudinal coordinate. Thus, due to the reasons disclosed above anddue to the dependency of the properties of the light spot on thelongitudinal coordinate, the combined signal Q typically is a monotonousfunction of the longitudinal coordinate and/or of the size of the lightspot such as the diameter or equivalent diameter of the light spot.Thus, as an example, specifically in case linear optical sensors areused, a simple quotient of the sensor signal s_(center) and the sumsignal s_(sum) Q=s_(center)/s_(sum) may be a monotonously decreasingfunction of the distance. Without wishing to be bound by this theory, itis believed that this is due to the fact that, in the preferred setupdescribed above, both the center signal s_(center) and the sum signals_(sum) decrease as a square function with increasing distance to thelight source, since the amount of light reaching the receiver unitdecreases. Therein, however, the center signal s_(center) decreases morerapidly than the sum signal s_(sum), since, in the optical setup as usedin the experiments, the light spot in the image plane grows and, thus,is spread over a larger area. The quotient of the center signal and thesum signal, thus, continuously decreases with increasing diameter of thelight beam or diameter of the light spot on the light-sensitive areas ofthe optical sensors of the matrix. The quotient, further, is typicallyindependent from the total power of the light beam, since the totalpower of the light beam forms a factor both in the center signal and inthe sum sensor signal. Consequently, the quotient Q may form a secondarysignal which provides a unique and unambiguous relationship between thecenter signal and the sum signal and the size or diameter of the lightbeam. Since, on the other hand, the size or diameter of the light beamis dependent on a distance between the sender unit, from which the lightbeam propagates towards the receiver unit, and the receiver unit itself,i.e. dependent on the longitudinal coordinate of the sender unit, aunique and unambiguous relationship between the center signal and thesum signal on the one hand and the longitudinal coordinate on the otherhand may exist. For the latter, reference e.g. may be made to one ormore of the above-mentioned prior art documents, such as WO 2014/097181A1. The predetermined relationship may be determined by analyticalconsiderations, such as by assuming a linear combination of Gaussianlight beams, by empirical measurements, such as measurements measuringthe combined signal and/or the center signal and the sum signal orsecondary signals derived thereof as a function of the longitudinalcoordinate of the sender unit, or both.

Thus, generally, the evaluation device may be configured for determiningthe longitudinal coordinate by evaluating the combined signal Q such asthe quotient signal. This determining may be a one-step process, such asby directly combining the center signal and the sum signal and derivingthe longitudinal coordinate thereof, or may be a multiple step process,such as by firstly deriving the combined signal from the center signaland the sum signal and, secondly, by deriving the longitudinalcoordinate from the combined signal. Both options, i.e. the option ofsteps c) and d) being separate and independent steps and the option ofsteps c) and d) being fully or partially combined, shall be comprised bythe present invention.

The evaluation device may be configured for using at least onepredetermined relationship between the combined signal and thelongitudinal coordinate. The predetermined relationship may be one ormore of an empiric relationship, a semi-empiric relationship and ananalytically derived relationship. The evaluation device may comprise atleast one data storage device for storing the predeterminedrelationship, such as a lookup list or a lookup table.

As outlined above, the optical sensors specifically may be or maycomprise photodetectors, preferably inorganic photodetectors, morepreferably inorganic semiconductor photodetectors, most preferablysilicon photodetectors. Specifically, the optical sensors may besensitive in the infrared spectral range. All of the optical sensors ofthe matrix or at least a group of the optical sensors of the matrixspecifically may be identical. Groups of identical optical sensors ofthe matrix specifically may be provided for different spectral ranges,or all optical sensors may be identical in terms of spectralsensitivity. Further, the optical sensors may be identical in sizeand/or with regard to their electronic or optoelectronic properties.

The matrix may be composed of independent optical sensors. Thus, amatrix of inorganic photodiodes may be composed. Alternatively, however,a commercially available matrix may be used, such as one or more of aCCD detector, such as a CCD detector chip, and/or a CMOS detector, suchas a CMOS detector chip.

Thus, generally, the optical sensors may form a sensor array or may bepart of a sensor array, such as the above-mentioned matrix. Thus, as anexample, the receiver unit may comprise an array of optical sensors,such as a rectangular array, having m rows and n columns, with m, n,independently, being positive integers. Preferably, more than one columnand more than one row is given, i.e. n>1, m>1. Thus, as an example, nmay be 2 to 16 or higher and m may be 2 to 16 or higher. Preferably, theratio of the number of rows and the number of columns is close to 1. Asan example, n and m may be selected such that 0.3≤m/n≤3, such as bychoosing m/n=1:1, 4:3, 16:9 or similar. As an example, the array may bea square array, having an equal number of rows and columns, such as bychoosing m=2, n=2 or m=3, n=3 or the like.

As further outlined above, the matrix specifically may be a rectangularmatrix having at least one row, preferably a plurality of rows, and aplurality of columns. As an example, the rows and columns may beoriented essentially perpendicular, wherein, with respect to the term“essentially perpendicular”, reference may be made to the definitiongiven above. Thus, as an example, tolerances of less than 20°,specifically less than 10° or even less than 5°, may be acceptable. Inorder to provide a wide range of view, the matrix specifically may haveat least 10 rows, preferably at least 500 rows, more preferably at least1000 rows. Similarly, the matrix may have at least 5 columns, preferablyat least 500 columns, more preferably at least 1000 columns. The matrixmay comprise at least 50 optical sensors, preferably at least 10000optical sensors, more preferably at least 500000 optical sensors. Thematrix may comprise a number of pixels in a multi-mega pixel range.Other embodiments, however, are feasible. Thus, as outlined above, insetups in which an axial rotational symmetry is to be expected, circulararrangements or concentric arrangements of the optical sensors of thematrix, which may also be referred to as pixels, may be preferred.

As further outlined above, preferably, the sensor element may beoriented essentially perpendicular to the optical axis of the receiverunit. With respect to the term “essentially perpendicular”, referencemay be made to the definition and the tolerances given above. Theoptical axis may be a straight optical axis or may be bent or evensplit, such as by using one or more deflection elements and/or by usingone or more beam splitters, wherein the essentially perpendicularorientation, in the latter cases, may refer to the local optical axis inthe respective branch or beam path of the optical setup.

As outlined above, by evaluating the center signal and the sum signal,the receiver unit may be enabled to determine the at least onelongitudinal coordinate of the sender unit including one or moretransversal coordinates and/or rotational coordinates, may be determinedby the evaluation device. Thus, as an example, one or more transversalsensors may be used for determining at least one transversal coordinate.As outlined above, the position of the at least one optical sensor fromwhich the center signal arises may provide information on the at leastone transversal coordinate of the sender unit, wherein, as an example, asimple lens equation may be used for optical transformation and forderiving the transversal coordinate. Additionally or alternatively, oneor more additional transversal sensors may be used and may be comprisedby the receiver unit. Various transversal sensors are generally known inthe art, such as the transversal sensors disclosed in WO 2014/097181 A1and/or other position-sensitive devices (PSDs), such as quadrant diodes,CCD or CMOS chips or the like. Additionally or alternatively, as anexample, the receiver unit may comprise one or more PSDs disclosed in R.A. Street: Technology and Applications of Amorphous Silicon,Springer-Verlag Heidelberg, 2010, pp. 346-349. Other embodiments arefeasible. These devices may generally also be implemented into thereceiver unit. As an example, a part of the light beam may be split offwithin the receiver unit, by at least one beam splitting element. Thesplit-off portion, as an example, may be guided towards a transversalsensor, such as a CCD or CMOS chip or a camera sensor, and a transversalposition of a light spot generated by the split-off portion on thetransversal sensor may be determined, thereby determining at least onetransversal coordinate. The evaluation device may be adapted to combinethe information of the longitudinal coordinate and the transversalcoordinate and to determine a position of the sender unit in space.

The receiver unit may be configured for evaluating a single light beamor a plurality of light beams. In case a plurality of light beamspropagates from the sender unit to the receiver unit, means fordistinguishing the light beams may be provided. Thus, the light beamsmay have different spectral properties, and the receiver unit maycomprise one or more wavelength selective elements for distinguishingthe different light beams. Each of the light beams may then be evaluatedindependently. The wavelength selective elements, as an example, may beor may comprise one or more filters, one or more prisms, one or moregratings, one or more dichroitic mirrors or arbitrary combinationsthereof. Further, additionally or alternatively, for distinguishing twoor more light beams, the light beams may be modulated in a specificfashion. Thus, as an example, the light beams may be frequencymodulated, and the sensor signals may be demodulated in order todistinguish partially the sensor signals originating from the differentlight beams, in accordance with their demodulation frequencies. Thesetechniques generally are known to the skilled person in the field ofhigh-frequency electronics. Generally, the evaluation device may beconfigured for distinguishing different light beams having differentmodulations.

The illumination source may be adapted to generate and/or to project acloud of points such that a plurality of illuminated regions isgenerated on the matrix of optical sensor, for example the CMOSdetector. Additionally, disturbances may be present on the matrix ofoptical sensor such as disturbances due to speckles and/or extraneouslight and/or multiple reflections. The evaluation device may be adaptedto determine at least one region of interest, for example one or morepixels illuminated by the light beam which are used for determination ofthe longitudinal coordinate. For example, the evaluation device may beadapted to perform a filtering method, for example, a blob-analysisand/or object recognition method.

In an embodiment, the two optical sensors may be arranged such that thegeometrical centers of the optical sensors are spaced apart from anoptical axis of the transfer device by different spatial offsets. Theevaluation device may be configured for determining at least onelongitudinal coordinate z by combining the at least two sensor signals.In this embodiment the optical sensors may be arranged such that thelight-sensitive areas of the optical sensors differ in their spatialoffset and/or their surface areas. The light-sensitive areas of theoptical sensors may overlap, as visible from the sender unit, or may notoverlap, i.e. may be placed next to each other without overlap. Thelight-sensitive areas may be spaced apart from each other or maydirectly be adjacent.

The receiver unit may comprise more than two optical sensors. In anycase, i.e. in the case of the receiver unit comprises precisely twooptical sensors and in the case of the receiver unit comprises more thantwo optical sensors, the optical sensors may comprise at least one firstoptical sensor being spaced apart from the optical axis by a firstspatial offset and at least one second optical sensor being spaced apartfrom the optical axis by a second spatial offset, wherein the firstspatial offset and the second spatial offset differ. In case furtheroptical sensors are provided, besides the first and second opticalsensors, these additional optical sensors may also fulfill the conditionor, alternatively, may be spaced apart from the optical axis by thefirst spatial offset, by the second spatial offset or by a differentspatial offset. The first and second spatial offsets, as an example, maydiffer by at least a factor of 1.2, more preferably by at least a factorof 1.5, more preferably by at least a factor of two. The spatial offsetsmay also be zero or may assume negative values, as long as theabove-mentioned conditions are fulfilled.

For example, the optical sensors may be partial diodes of a segmenteddiode, with a center of the segmented diode being off-centered from theoptical axis of the transfer device. The optical sensors may be partialdiodes of a bi-cell or quadrant diode and/or comprise at least one CMOSsensor. As used herein, the term “partial diode” may comprise severaldiodes that are connected in series or in parallel. This example israther simple and cost-efficiently realizable. Thus, as an example,bi-cell diodes or quadrant diodes are widely commercially available atlow cost, and driving schemes for these bi-cell diodes or quadrantdiodes are generally known. As used herein, the term “bi-cell diode”generally refers to a diode having two partial diodes in one packaging.Bi-cell and quadrant diodes may have two or four separate lightsensitive areas, in particular two or four active areas. As an example,the bi-cell diodes may each form independent diodes having the fullfunctionality of a diode. As an example, each of the bi-cell diodes mayhave a square or rectangular shape, and the two diodes may be placed inone plane such that the two partial diodes, in total, form a 1×2 or 2×1matrix having a rectangular shape. In the present invention, however, anew scheme for evaluating the sensor signals of the bi-cell diodes andquadrant diode is proposed, as will be outlined in further detail below.Generally, however, the optical sensors specifically may be partialdiodes of a quadrant diode, with a center of the quadrant diode beingoff-centered from the optical axis of the transfer device. As usedherein, the term “quadrant diode” generally refers to a diode havingfour partial diodes in one packaging. As an example, the four partialdiodes may each form independent diodes having the full functionality ofa diode. As an example, the four partial diodes may each have a squareor rectangular shape, and the four partial diodes may be placed in oneplane such that the four partial diodes, in total, form a 2×2 matrixhaving a rectangular or square shape. In a further example, the fourpartial diodes, in total, may form a 2×2 matrix having a circular orelliptical shape. The partial diodes, as an example, may be adjacent,with a minimum separation from one another. As an example, the center ofthe bi-cell diodes, which may be an intersection of the geometricalcenters of the optical sensors of the bi-cell diode, may be off-centeredfrom the optical axis by at least 0.01 mm, more preferably by at least0.1 mm, more preferably by at least 1.0 mm or even 2.0 mm. Thus, as afurther example, the center of the center of the bi-cell diodes may beoff-centered from the optical axis by a factor of at least 0.0001 timesthe maximum extent of the light sensitive area orthogonal to the opticalaxis, preferably by a factor of at least 0.001, more preferably by afactor of at least 0.005 times the maximum extent of the light sensitivearea orthogonal to the optical axis.

In case a quadrant diode is used, having a 2×2 matrix of partial diodes,the center of the quadrant diode specifically may be off-centered oroffset from the optical axis of the transfer device of the receiverunit. Thus, as an example, the center of the quadrant diodes, which maybe an intersection of the geometrical centers of the optical sensors ofthe quadrant diode, may be off-centered from the optical axis by atleast 0.01 mm, more preferably by at least 0.1 mm, more preferably by atleast 1.0 mm or even 2.0 mm. Thus, as a further example, the center ofthe center of the quadrant diodes may be off-centered from the opticalaxis by a factor of at least 0.0001 times the maximum extent of thelight sensitive area orthogonal to the optical axis, preferably by afactor of at least 0.001, more preferably by a factor of at least 0.005times the maximum extent of the light sensitive area orthogonal to theoptical axis. Similarly, when using other types of optical sensorssetups having a plurality of optical sensors, an overall center of theoptical sensors may be offset from the optical axis by the samedistance.

Generally, the light-sensitive areas of the optical sensors may have anarbitrary surface area or size. Preferably, however, specifically inview of a simplified evaluation of the sensor signals, thelight-sensitive areas of the optical sensors are substantially equal,such as within a tolerance of less than 10%, preferably less than 5% oreven less than 1%. This, specifically, is the case in typicalcommercially available quadrant diodes.

Specifically, the evaluation device may be configured to determine theat least one longitudinal coordinate z of the sender unit using at leastone known, determinable or predetermined relationship between sensorsignals and/or any secondary signal derived thereof and the longitudinalcoordinate. Thus, the evaluation device may be configured fordetermining at least one combined sensor signal out of the at least twosensor signals, i.e. of the at least one sensor signal of at least onefirst optical sensor and out of the at least one sensor signal of atleast one second optical sensor. As generally used herein, the term“combine” generally may refer to an arbitrary operation in which two ormore components such as signals are one or more of mathematically mergedin order to form at least one merged combined signal and/or compared inorder to form at least one comparison signal or comparison result. As anexample, Q may simply be determined as Q=s₁/s₂ or Q=s₂/s₁, with s₁denoting a first one of the sensor signals and s₂ denoting a second oneof the sensor signals. Additionally or alternatively, Q may bedetermined as Q=j·s₁/k·s₂ or Q=k·s₂/j·s₁, with j and k being realnumbers which, as an example, may be predetermined or determinable.Additionally or alternatively, Q may be determined asQ=(j·s₁+k·s₂)/(p·s₁+q·s₂), with j, k, p and q being real numbers which,as an example, may be predetermined or determinable. As a simple examplefor the latter, Q may be determined as Q=s₁/(s₁+s₂), or, as a furtherexample, Q may be determined as Q=(s₁−s₂)/(s₁+s₂). Other quotientsignals are feasible. Thus, as an example, in case more than two opticalsensors are provided, the above-mentioned quotient formation may takeplace between two of the sensor signals generated by these opticalsensors or may take place between more than two of the sensor signals.Thus, instead of using the first one of the sensor signals and thesecond one of the sensor signals in the formulae given above, combinedsensor signals may be used for quotient formation.

In typical setups, commercially available quadrant diodes such asquadrant photodiodes are used for positioning, i.e. for adjusting and/ormeasuring a transversal coordinate of a light spot in the plane of thequadrant photodiode. Thus, as an example, laser beam positioning byusing quadrant photodiodes is well known. According to a typicalprejudice, however, quadrant photodiodes are used for xy-positioning,only. According to this assumption, quadrant photodiodes are notsuitable for measuring distances. The above-mentioned findings, however,using an off-centered quadrant photodiode with regard to an optical axisof the receiver unit, show otherwise, as will be shown in furthermeasurements below. Thus, as indicated above, in quadrant photodiodes,the asymmetry of the spot can be measured by shifting the quadrant diodeslightly off-axis, such as by the above-mentioned offset. Thereby, amonotonously z-dependent function may be generated, such as by formingthe combined signal Q of two or more of the sensor signals of two ormore partial photodiodes, i.e. quadrants, of the quadrant photodiode.Therein, in principle, only two photodiodes are necessary for themeasurement. The other two diodes may be used for noise cancellation orto obtain a more precise measurement. In addition or as an alternativeto using a quadrant diode or quadrant photodiode, other types of opticalsensors may be used. Thus, as will be shown in further detail below,staggered optical sensors may be used.

The use of quadrant diodes provides a large number of advantages overknown optical detectors. Thus, quadrant diodes are used in a largenumber of applications in combination with LEDs or active targets andare widely commercially available at very low price, with variousoptical properties such as spectral sensitivities and in various sizes.No specific manufacturing process has to be established, sincecommercially available products may be implemented into the receiverunit. In case a quadrant diode is used, the quadrant diode may also beused for additional purposes. Thus, the quadrant diode may also be usedfor conventional x-y-measurements of a light spot, as generally known inthe art of optoelectronics and laser physics. Thus, as an example, thelens or receiver unit position can be adjusted using the conventionalxy-position information of the quadrant diode to optimize the positionof the spot for the distance measurement. As a practical example, thelight spot, initially, may be located right in the center of thequadrant diode, which typically does not allow for the above-mentioneddistance measurement using the combined signal Q. Thus, firstly,conventional quadrant photodiode techniques may be used foroff-centering a position of the light spot on the quadrant photodiode,such that, e.g., the spot position on the quadrant diode is optimal forthe measurement. Thus, as an example, the different off-centering of theoptical sensors may simply be a starting point for movement of theoptical sensors relative to the optical axis such that the light spot isoff-centered with respect to the optical axis and with respect to ageometrical center of the array of the optical sensors.

Thus, generally, the optical sensors may form a sensor array or may bepart of a sensor array, such as the above-mentioned quadrant diode.Thus, as an example, the receiver unit may comprise the array of opticalsensors, such as a rectangular array, having m rows and n columns, withm, n, independently, being positive integers. Preferably, more than onecolumn and more than one row is given, i.e. n>1, m>1. Thus, as anexample, n may be 2 to 16 or higher and m may be 2 to 16 or higher.Preferably, the ratio of the number of rows and the number of columns isclose to 1. As an example, n and m may be selected such that 0.3≤m/n≤3,such as by choosing m/n=1:1, 4:3, 16:9 or similar. As an example, thearray may be a square array, having an equal number of rows and columns,such as by choosing m=2, n=2 or m=3, n=3 or the like. The case m=2, n=2is the case of the quadrant diode or quadrant optical sensor, which, forpractical reasons, is one of the preferred cases, since quadrantphotodiodes are widely available.

As a starting point, a geometrical center of the optical sensors withinthe array may be off-centered from the optical axis, such as by theabove-mentioned offset. The sensor array specifically may be movablerelative to the optical axis, for example along a gradient, preferablyautomatically, such as by moving the sensor array, e.g. in a planeperpendicular to the optical axis, and/or by moving the optical axisitself, e.g. shifting the optical axis in a parallel shift and/ortilting the optical axis. Thus, the sensor array may be shifted in orderto adjust a position of a light spot generated by the light beam in theplane of the sensor array. Additionally or alternatively, the opticalaxis may be shifted and/or tilted by using appropriate elements, such asby using one or more deflection elements and/or one or more lenses. Themovement, as an example, may take place by using one or more appropriateactuators, such as one or more piezo actuators and/or one or moreelectromagnetic actuators and/or one or more pneumatic or mechanicalactuators, which, e.g., move and/or shift the array and/or move and/orshift and/or tillage one or more optical elements in the beam path inorder to move the optical axis, such as parallel shifting the opticalaxis and/or tilting the optical axis. The evaluation device specificallymay be adjusted to control a relative position of the sensor array tothe optical axis, e.g. in the plane perpendicular to the optical axis.An adjustment procedure may take place in that the evaluation device isconfigured for, firstly, determining the at least one transversalposition of a light spot generated by the light beam on the sensor arrayby using the sensor signals and for, secondly, moving the array relativeto the optical axis, such as by moving the array and/or the opticalaxis, e.g. by moving the array in the plane to the optical axis untilthe light spot is off-centered and/or by tilting a lens until the lightspot is off-centered. As used therein, a transversal position may be aposition in a plane perpendicular to the optical axis, which may also bereferred to as the x-y-plane. For the measurement of the transversalcoordinate, as an example, the sensor signals of the optical sensors maybe compared. As an example, in case the sensor signals are found to beequal and, thus, in case it is determined that the light spot is locatedsymmetrically with respect to the optical sensors, such as in the centerof the quadrant diodes, a shifting of the array and/or a tilting of alens may take place, in order to off-center the light spot in the array.Thus, as outlined above, the off-centering of the array from the opticalaxis, such as by off-centering the center of the quadrant photodiodefrom the optical axis, may simply be a starting point in order to avoidthe situation which is typical, in which the light spot is located onthe optical axis and, thus, is centered. By off-centering the arrayrelative to the optical axis, thus, the light spot should beoff-centered. In case this is found not to be true, such that the lightspot, incidentally, is located in the center of the array and equallyilluminates all optical sensors, the above-mentioned shifting of thearray relative to the optical axis may take place, preferablyautomatically, in order to off-center the light spot on the array.Thereby, a reliable distance measurement may take place.

Further, the use of the above-mentioned combined signal Q is a veryreliable method for distance measurements. Since, on the other hand, thesize or diameter of the light beam is dependent on a distance betweenthe sender unit, from which the light beam propagates towards thereceiver unit, and the receiver unit itself, i.e. dependent on thelongitudinal coordinate of the sender unit, a unique and unambiguousrelationship between the first and second sensor signals and thelongitudinal coordinate may exist. For the latter, reference e.g. may bemade to one or more of the above-mentioned prior art documents, such asWO 2014/097181 A1. The predetermined relationship may be determined byanalytical considerations, such as by assuming a linear combination ofGaussian light beams, by empirical measurements, such as measurementsmeasuring the first and second sensor signals or a secondary signalderived thereof as a function of the longitudinal coordinate, or both.

As outlined above, specifically, quadrant photodiodes may be used. As anexample, commercially available quadrant photodiodes may be integratedin order to provide four optical sensors, such as one or more quadrantphotodiodes available from Hamamatsu Photonics Deutschland GmbH, D-82211Herrsching am Ammersee, Germany, such as quadrant Si PIN photodiodes ofthe type S4349, which are sensitive in the UV spectral range to the nearIR spectral range. In case an array of optical sensors is used, thearray may be a naked chip or may be an encapsulated array, such asencapsulated in a TO-5 metal package. Additionally or alternatively, asurface mounted device may be used, such as TT Electronics OPR5911available from TT Electronics plc, Fourth Floor, St Andrews House, WestStreet Woking Surrey, GU21 6EB, England. It shall be noted that otheroptical sensors may also be used.

Further, it shall be noted that, besides the option of using preciselyone quadrant photodiode, two or more quadrant photodiodes may also beused. Thus, as an example, a first quadrant photodiode may be used forthe distance measurement, as described above, providing the two or moreoptical sensors. Another quadrant photodiode may be used, e.g. in asecond partial beam path split off from the beam path of the firstquadrant photodiode, for a transversal position measurement, such as forusing at least one transversal coordinate x and/or y. The secondquadrant photodiode, as an example, may be located on-axis with respectto the optical axis.

Further, it shall be noted that, besides the option of using one or morequadrant photodiodes, one or more quadrant photodiodes or furtherphotodiode arrays may also be replaced or mimicked by separatedphotodiodes that are arranged or assembled close to each other,preferably in a symmetric shape such as a rectangular matrix, such as a2×2 matrix. However further arrangements are feasible. In such anarrangement or assembly, the photodiodes may be arranged or assembled ina housing or mount, such as all photodiodes in a single housing or mountor groups of photodiodes in one housing or mount, or each of thephotodiodes in a separate housing or mount. Further, the photodiodes mayalso be assembled directly on a circuit board. In such arrangements orassemblies, photodiodes may be arranged as such that the separationbetween the active area of the photodiodes, has a distinct value lessthan one centimeter, preferably less than one millimeter, morepreferably as small as possible. Further, to avoid optical reflexes,distortions, or the like that may deteriorate the measurement, the spacebetween the active areas may be either empty or filled with a material,preferably with a light absorbing material such as a black polymer, suchas black silicon, black polyoxymethylene, or the like, more preferablyoptically absorbing and electrically insulating material, such as blackceramics or insulating black polymers such as black silicon, or thelike. Further, the distinct value of the photodiode separation may alsobe realized by adding a distinct building block between the photodiodessuch as a plastic separator. Further embodiments are feasible. Thereplacement of quadrant photodiodes by single diodes arranged in asimilar setup such as in a 2×2 rectangular matrix with minimal distancebetween the active areas may further minimize the costs for the opticaldetector. Further, two or more diodes from a quadrant diode may beconnected in parallel or in series to form a single light sensitivearea. The receiver unit furthermore may comprise at least one angledependent optical element adapted to adapt the light beam travellingfrom the sender unit to the receiver unit to have a beam profiledepending on an angle of incidence of the light beam when impinging onthe angle dependent optical element. The angle dependent optical elementmay comprise at least one optical element selected from the groupconsisting of: at least one optical fiber, in particular at least onemultifurcated optical fiber, in particular at least one bifurcatedoptical fiber; at least one lens array arranged in at least one planeperpendicular to an optical axis of the receiver unit, in particular atleast one microlens array; at least one optical interference filter; atleast one nonlinear optical element, in particular one birefringentoptical element; at least one liquid crystal filter; at least onepolarization filter. Each of the optical sensor may be designed togenerate at least one sensor signal in response to an illumination ofits respective light-sensitive area by the light beam generated by theangle dependent optical element. The evaluation device may be configuredfor determining at least one longitudinal coordinate z of the senderunit by evaluating the combined signal Q from the sensor signals.

As used herein, the term “angle dependent optical element” refers to anoptical element adapted to adapt the light beam generated by the senderunit to have a beam profile depending on the angle of incidence whenimpinging on the angle dependent optical element. In particular, theangle dependent optical element may be adapted to influence and/orchange and/or adjust the beam profile of the incident light beam. Forexample, the angle dependent optical element may have one or more ofangle dependent transmission properties, angle dependent reflectionproperties or angle dependent absorption properties. The angle ofincidence may be measured with respect to an optical axis of the angledependent optical element.

An electromagnetic wave impinging on a first side, for example a surfaceand/or an entrance, of the angle dependent optical element may bepartly, depending on the properties of the angle dependent opticalelement, absorbed and/or reflected and/or transmitted. The term“absorption” refers to a reduction of power and/or intensity of theincident light beam by the angle dependent optical element. For example,the power and/or intensity of the incident light beam may be transformedby the angle dependent optical element to heat or another type ofenergy. As used herein, the term “transmission” refers to a part of theelectromagnetic wave which is measurable outside the angle dependentoptical element in a half-space with angles from 90° and higher withrespect to the optical axis. For example, transmission may be aremaining part of the electromagnetic wave impinging on the first sideof the angle dependent optical element, penetrating the angle dependentoptical element and leaving the angle dependent optical element at asecond side, for example an opposite side and/or an exit. The term“reflection” refers to a part of the electromagnetic wave which ismeasurable outside the angle dependent optical element in a half-spacewith angles below 90° with respect to the optical axis. For example,reflection may be a change in direction of a wavefront of the incidentlight beam due to interaction with the angle dependent optical element.

The total power of the electromagnetic wave impinging on the angledependent optical element may be distributed by the angle dependentoptical element in at least three components, i.e. an absorptioncomponent, a reflection component and a transmission component. A degreeof transmission may be defined as power of the transmission componentnormalized by the total power of the electromagnetic wave impinging onthe angle dependent optical element. A degree of absorption may bedefined as power of the absorption component normalized by the totalpower of the electromagnetic wave impinging on the angle dependentoptical element. A degree of reflection may be defined as power of thereflection component normalized by the total power of theelectromagnetic wave impinging on the angle dependent optical element.

As used herein, “angle dependent transmission” refers to the fact thatthe degree of transmission depends on the angle of incidence at whichthe incident light beam impinges on the angle dependent optical element.The angle dependent optical element may be arranged in the direction ofpropagation behind at least one transfer device. The angle dependentoptical element and the transfer device may be arranged such that thelight beam passes through the transfer device before impinging on theangle dependent optical element. The angle dependent optical element maybe arranged as such, that the light beam impinges on the angle dependentoptical element between the transfer device and the focal point of thetransfer device. Use of at least one transfer device allows to furtherenhance robustness of the measurement of the longitudinal coordinate.The transfer device may, for example, comprise at least one collimatinglens. The angle dependent optical element may be designed to weaken raysimpinging with larger angles compared to rays impinging with a smallerangle. For example, the degree of transmission may be highest for lightrays parallel to the optical axis, i.e. at 0°, and may decrease forhigher angles. In particular, at at least one cut-off angle the degreeof transmission may steeply fall to zero. Thus, light rays having alarge angle of incidence may be cut-off.

As used herein, the term “angle dependent absorption” refers to the factthat the degree of absorption depends on the angle of incidence at whichthe incident light beam impinges on the angle dependent optical element.As used herein, the term “angle dependent absorption” refers to the factthat a degree of absorption depends on the angle of incidence at whichthe incident light beam impinges on the angle dependent optical element.For example, photon energy and/or intensity of the light beampropagating from the sender unit to the receiver unit may be reduceddepending on the angle of incidence. As used herein, the term “angledependent reflection” refers to the fact that the degree of reflectiondepends on the angle of incidence at which the incident light beamimpinges on the angle dependent optical element.

For example, the angle dependent optical element comprises at least oneoptical fiber. Specifically, the angle dependent optical elementcomprises at least one optical measurement fiber. The optical fiber maybe designed such that the degree of transmission may be highest forincoming light rays parallel, i.e. at an angle of 0°, to the opticalfiber, neglecting reflection effects. The optical fiber may be designedsuch that for higher angles, for example angles from 1° to 10°, thedegree of transmission may decrease smoothly to around 80% of the degreeof transmission for parallel light rays and may remain at this levelconstantly up to an acceptance angle of the optical fiber. As usedherein, the term “acceptance angle” may refer to an angle above whichtotal reflection within the optical fiber is not possible such that thelight rays are reflected out of the optical fiber. The optical fiber maybe designed that at the acceptance angle, the degree of transmission maysteeply fall to zero. Light rays having a large angle of incidence maybe cut-off.

The optical fiber may be adapted to transmit at least parts of theincident light beam which are not absorbed and/or reflected, between twoends of the optical fiber. The optical fiber may have a length and maybe adapted to permit transmission over a distance. The optical fiber maycomprise at least one material selected from the group consisting of:silica, aluminosilicate glass, germane silicate glass, fluorozirconate,rare earth doped glass, fluoride glass, chalcogenide glasses, sapphire,doped variants, especially for silica glass, phosphate glass, PMMA,polystyrene, fluoropolymers such as poly(perfluoro-butenylvinyl ether),or the like. The optical fiber may be a single or multi-mode fiber. Theoptical fiber may be a step index fiber, a polarizing fiber, apolarization maintaining fiber, a plastic optical fiber or the like. Theoptical fiber may comprise at least one fiber core which is surroundedby at least one fiber cladding having a lower index of refraction as thefiber core. The fiber cladding may also be a double or multiplecladding. The fiber cladding may comprise a so-called outer jacket. Thefiber cladding may be coated by a so-called buffer adapted to protectthe optical fiber from damages and moisture. The buffer may comprise atleast one UV-cured urethane acrylate composite and/or at least onepolyimide material. In one embodiment, a refractive index of the fibercore may be higher than the refractive index of the fiber claddingmaterial and the optical fiber may be adapted to guide the incominglight beam by total internal reflection below the angle of acceptance.In one embodiment, the optical fiber may comprise at least one hollowcore fiber, also called photonic bandgap fiber. The hollow-core fibermay be adapted to guide the incoming light beam essentially within aso-called hollow region, wherein a minor portion of the light beam islost due to propagation into the fiber cladding material.

The optical fiber may comprise one or more fiber connectors at the endof the fiber. The optical fiber may comprise end caps such as corelessend caps. The optical fiber may comprise one or more of a fiber coupler,a fiber Bragg grating, a fiber polarizer, a fiber amplifier, a fibercoupled diode laser, a fiber collimator, a fiber joint, a fibersplicing, a fiber connector, a mechanical splicing, a fusion splicing,or the like. The optical fiber may comprise a polymer coating.

The optical fiber may comprise at least two or more fibers. The opticalfiber may be at least one multifurcated optical fiber, in particular atleast one bifurcated optical fiber. For example, the bifurcated opticalfiber may comprise two fibers, in particular at least one first fiberand at least one second fiber. The first fiber and the second fiber maybe arranged close to each other at an entrance end of the bifurcatedoptical fiber and may split into two legs separated by a distance at anexit end of the bifurcated optical fiber. The first and second fiber maybe designed as fibers having identical properties or may be fibers ofdifferent type. The first fiber may be adapted to generate at least onefirst transmission light beam and the second fiber may be adapted togenerate at least one second transmission light beam. The bifurcatedoptical fiber may be arranged such that the incident light beam mayimpinge at a first angle of incidence into the first fiber and at asecond angle of incidence, different from the first angle, into thesecond fiber, such that the degree of transmission is different for thefirst transmission light beam and the second transmission light beam.One of the optical sensors may be arranged at an exit end of the firstfiber and the other optical sensor may be arranged at an exit end of thesecond fiber. The optical fiber may comprise more than two fibers, forexample three, four or more fibers. For example, the multifurcated maycomprise multiple fibers wherein each fiber may comprise at least one ofa core, a cladding, a buffer, a jacket, and one or more fibers maypartially or entirely be bundled by a further jacket such as a polymerhose to ensure that the fibers stay close to each other such as at oneend of the fiber. All optical fibers may have the same numericalaperture. All optical fibers may be arranged as such, that the lightbeam propagating from the sender unit to the receiver unit impinges onall of the optical fibers between the transfer device and the focalpoint of the transfer device. The optical fibers may be arranged assuch, that the position along the optical axis where the light beampropagating from the sender unit to the receiver unit impinges on theoptical fibers is identical for all optical fibers. Other arrangementsmay be possible.

The receiver unit may comprise a plurality of optical fibers, forexample a plurality of single optical fibers or a plurality ofmultifurcated optical fibers. For example, the optical fibers may bearranged in a bundle of optical fibers. For example, the receiver unitmay comprise a plurality of single optical fibers, for example opticalfibers having identical properties. The optical fibers, i.e. the singleoptical fibers or multifurcated optical fibers, may be arranged suchthat the incident light beam may impinge at different angles ofincidence into each of the optical fibers such that the degree oftransmission is different for each of the optical fibers. At the exitends of each optical fiber at least one optical sensor may be arranged.Alternatively, at least two or more of the optical fibers may use thesame optical sensor. The optical sensors at the end of the opticalfibers may be arranged as such that at least 80%, preferably at least90%, more preferably at least 99% of the luminance power of the lightbeams exiting the optical fiber towards the optical sensors impinge onat least one optical sensor. In case the angle dependent optical elementis an optical fiber, the relevant position of the angle dependentoptical element and/or the optical sensor relative to the transferdevice to optimize the combined signal Q may be given by the positionwhere the light beam travelling from the sender unit to the receiverunit impinges on the angle dependent optical element. In particular, theposition relative to the transfer device where the light beam travellingfrom the sender unit to the receiver unit impinges on the optical fibermay be optimized to obtain a combined signal Q with a high dynamicrange. Further, concerning the optimization of the optical setup, incase the angle dependent optical element is an optical fiber, theposition where the light beam impinges on the optical fiber correspondsto the position where the light beam impinges on the optical sensor incase the angle dependent optical element is not a fiber, such as aninterference filter.

In a further aspect, the present invention discloses a method foroptically surveilling at least one area by using at least one devicecomprising a sender unit and a receiver unit. The device may be a deviceaccording to the present invention, such as according to one or more ofthe embodiments referring to a device for optically surveillance asdisclosed above or as disclosed in further detail below. Still, othertypes of devices may be used. The method comprises the following methodsteps, wherein the method steps may be performed in the given order ormay be performed in a different order. Further, one or more additionalmethod steps may be present which are not listed. Further, one, morethan one or even all of the method steps may be performed repeatedly.

The method comprises the following steps:

-   -   providing a sender unit having at least one illumination source,        wherein the illumination source is designed to generate at least        one light beam, each light beam having a beam profile, wherein        each light beam is designated for propagating to the receiver        unit, thereby traversing the at least one area for surveillance;    -   providing a receiver unit having at least one transfer device,        at least two optical sensors and an evaluation device, wherein        the transfer device has at least one focal length in response to        the at least one incident light beam propagating from the        illumination source to at least two optical sensors, wherein the        transfer device has an optical axis, wherein the transfer device        constitutes a coordinate system, wherein a longitudinal        coordinate I is a coordinate along the optical axis and wherein        d is a spatial offset from the optical axis, wherein each        optical sensor has at least one light sensitive area, wherein        each optical sensor is designed to generate at least one sensor        signal in response to an illumination of its respective        light-sensitive area by the light beam, wherein two of the        optical sensors are arranged in a manner that the        light-sensitive areas of the two optical sensors differ in at        least one of: their longitudinal coordinate, their spatial        offset, or their surface areas;    -   generating the at least one light beam for illuminating each of        the light-sensitive areas of the at least two optical sensors of        the receiver unit with the light beam propagating from the        sender unit to the receiver unit, thereby traversing at least        one area for surveillance, wherein, thereby, each of the        light-sensitive areas generates at least one sensor signal; and    -   evaluating the sensor signals, thereby, generating an output by        monitoring at least one change of, firstly, the beam profile of        the at least one light beam upon traversing the at least one        area of surveillance by evaluating the sensor signals and,        further, of at least one component of a location of the sender        unit, wherein the component is determined with respect to the        coordinate system of the transfer device, by evaluating a        combined signal Q from the sensor signals.

The method may further comprise initiating at least one action based onthe output, wherein the at least one action is selected format least oneof: providing at least one information, generating at least one warning,inducing at least one instruction, changing an output signal. Fordetails, options and definitions, reference may be made to the device asdiscussed above.

In a further aspect of the present invention, use of the deviceaccording to the present invention, such as according to one or more ofthe embodiments given above or given in further detail below, isproposed, for a purpose of use, selected from the group consisting of:monitoring at least one apparatus located in a surveillance area;distinguishing between a willful manipulation from an not intentionalmanipulation related to the at least one apparatus located in thesurveillance area; indicating a failure of a safety function.

With respect to further uses of the device according to the presentinvention reference is made to in WO 2018/091649 A1, WO 2018/091638 A1and WO 2018/091640, the content of which is included by reference.

Overall, in the context of the present invention, the followingembodiments are regarded as preferred:

Embodiment 1: A device for optically surveilling at least one area, thedevice comprising a sender unit and a receiver unit,

-   -   wherein the sender unit has at least one illumination source,        wherein the illumination source is designed to generate at least        one light beam having a beam profile, wherein each light beam is        designated for propagating to the receiver unit, thereby        traversing at least one area for surveillance;    -   wherein the receiver unit comprises        -   at least one transfer device, wherein the transfer device            has at least one focal length in response to the at least            one incident light beam propagating from the illumination            source to at least two optical sensors, wherein the transfer            device has an optical axis, wherein the transfer device            constitutes a coordinate system, wherein a longitudinal            coordinate I is a coordinate along the optical axis and            wherein d is a spatial offset from the optical axis,        -   at least two optical sensors, wherein each optical sensor            has at least one light sensitive area, wherein each optical            sensor is designed to generate at least one sensor signal in            response to an illumination of its respective            light-sensitive area by the light beam, wherein two of the            optical sensors are arranged in a manner that the            light-sensitive areas of the two optical sensors differ in            at least one of: their longitudinal coordinate, their            spatial offset, or their surface areas; and        -   at least one evaluation device, wherein the evaluation            device is being configured for generating an output by            monitoring at least one change of, firstly, the beam profile            of the at least one light beam upon traversing the at least            one area of surveillance by evaluating the sensor signals            and, further, of at least one component of a location of the            sender unit, wherein the component is determined with            respect to the coordinate system of the transfer device, by            evaluating a combined signal Q from the sensor signals.

Embodiment 2: The device according to the preceding embodiment, whereinthe evaluation device is further configured for initiating at least oneaction based on the output, wherein the at least one action is selectedfrom at least one of: providing at least one information, generating atleast one warning, inducing at least one instruction, changing an outputsignal Embodiment 3: The device according to the preceding embodiment,wherein the evaluation device is further configured for assigning theinformation to a time of event and for storing a combination of theinformation with the time of event in an information log.

Embodiment 4: The device according to any one of the two precedingembodiments, wherein the warning comprises a visual, an audible or ahaptic warning signal.

Embodiment 5: The device according to any one of the three precedingembodiments, wherein the instruction comprises initiating a shutdown ofat least one apparatus.

Embodiment 6: The device according to any one of the precedingembodiments, wherein the sender unit further comprises at least onemodulation source, the modulation source being configured for generatinga modulation pattern in a manner that the modulation source impinges theillumination source to generate at least one light beam carrying themodulation pattern.

Embodiment 7: The device according to the preceding embodiment, whereinthe modulation pattern is selected from the group consisting of: apseudo random modulation pattern, an Aiken code, a BCD code, a Gillhamcode, a Stibitz code, a one-hot code, and a gray code.

Embodiment: 8 The device according to any one of the two precedingembodiments, wherein the modulation pattern is selected from the groupconsisting of: a rectangular pulse pattern, 50:50 rectangular pattern,sinusoidal pattern, periodic pulse patterns.

Embodiment 9: The device according to any one of the two precedingembodiments, wherein the sender unit comprises at least two illuminationsources, wherein each of the illumination sources is designed for beingmodulated by an individual modulation pattern, the individual modulationpattern of two illumination sources being different with respect to eachother.

Embodiment 10: The device according to any one of the three precedingembodiments, wherein the sender unit comprises an individual modulationsource for each illumination source, or wherein the sender unit furthercomprises a multiplexer being designated for switching an individualimpingement of at least two of the illumination sources by a singlemodulation source.

Embodiment 11: The device according to any one of the two precedingembodiments, wherein the evaluation device is designated for assigningan individual modulation pattern to an individual illumination source.

Embodiment 12: The device according to any one of the precedingembodiments, further comprising a connection between the sender unit andthe receiver unit, wherein the connection is designed for providingsynchronization between the sender unit and the receiver unit.

Embodiment 13: The device according to any one of the precedingembodiments, further comprising at least one reflective target designedfor being impinged by the at least one light beam propagating from theat least one illumination source to the at least two optical sensors.

Embodiment 14: The device according to any one of the precedingembodiments, wherein two of the optical sensors are arranged as

-   -   at least one first optical sensor having a first light-sensitive        area, wherein the first optical sensor is configured to generate        at least one first sensor signal in response to an illumination        of the first light-sensitive area by the light beam propagating        from the sender unit to the receiver unit; and    -   at least one second optical sensor having a second        light-sensitive area, wherein the second optical sensor is        configured to generate at least one second sensor signal in        response to an illumination of the second light-sensitive area        by the light beam, wherein the first light-sensitive area is        smaller than the second light-sensitive area;    -   wherein the evaluation device is being configured for generating        the output by evaluating the first and second sensor signals.

Embodiment 15: The device according to the preceding embodiment, whereinthe evaluation device is further designed for generating the at leastone output by monitoring a change of the first sensor signal or of thesecond sensor signal.

Embodiment 16: The device according to any one of the precedingembodiments, wherein the sender unit and the receiver unit are arrangedwith respect to each other in a manner that the sensor signal of atleast one of the optical sensors is a highest sensor signal.

Embodiment 17: The device according to any one of the precedingembodiments, wherein the evaluation device is further designed forgenerating the output by using at least one reference beam profile forthe at least one light beam generated by the illumination source and atleast one reference component for the at least one component of thelocation of the sender unit.

Embodiment 18: The device according to the preceding embodiment, whereinthe at least one reference beam profile and the at least one referencecomponent are stored during a teaching phase.

Embodiment 19: A method for optically surveilling at least one area byusing at least one device comprising a sender unit and a receiver unit,the method comprising the following steps:

-   -   providing a sender unit having at least one illumination source,        wherein the illumination source is designed to generate at least        one light beam, each light beam having a beam profile, wherein        each light beam is designated for propagating to the receiver        unit, thereby traversing the at least one area for surveillance;    -   providing a receiver unit having at least one transfer device,        at least two optical sensors and an evaluation device, wherein        the transfer device has at least one focal length in response to        the at least one incident light beam propagating from the        illumination source to at least two optical sensors, wherein the        transfer device has an optical axis, wherein the transfer device        constitutes a coordinate system, wherein a longitudinal        coordinate I is a coordinate along the optical axis and wherein        d is a spatial offset from the optical axis, wherein each        optical sensor has at least one light sensitive area, wherein        each optical sensor is designed to generate at least one sensor        signal in response to an illumination of its respective        light-sensitive area by the light beam, wherein two of the        optical sensors are arranged in a manner that the        light-sensitive areas of the two optical sensors differ in at        least one of: their longitudinal coordinate, their spatial        offset, or their surface areas;    -   generating the at least one light beam for illuminating each of        the light-sensitive areas of the at least two optical sensors of        the receiver unit with the light beam propagating from the        sender unit to the receiver unit, thereby traversing at least        one area for surveillance, wherein, thereby, each of the        light-sensitive areas generates at least one sensor signal; and    -   evaluating the sensor signals, thereby, generating an output by        monitoring at least one change of, firstly, the beam profile of        the at least one light beam upon traversing the at least one        area of surveillance by evaluating the sensor signals and,        further, of at least one component of a location of the sender        unit, wherein the component is determined with respect to the        coordinate system of the transfer device, by evaluating a        combined signal Q from the sensor signals.

Embodiment 20: The method according to the preceding embodiment, furthercomprising initiating at least one action based on the output, whereinthe at least one action is selected from at least one of: providing atleast one information, generating at least one warning, inducing atleast one instruction, changing an output signal.

Embodiment 21: A use of a device according to any one of the precedingembodiments referring to a device, for a purpose of use, selected fromthe group consisting of: monitoring at least one apparatus located in asurveillance area; distinguishing between a willful manipulation from anot intentional manipulation related to the at least one apparatuslocated in the surveillance area; indicating a failure of a safetyfunction.

BRIEF DESCRIPTION OF THE FIGURES

Further optional details and features of the invention are evident fromthe description of preferred exemplary embodiments which follows inconjunction with the dependent claims.

In this context, the particular features may be implemented in anisolated fashion or in combination with other features. The invention isnot restricted to the exemplary embodiments. The exemplary embodimentsare shown schematically in the figures.

Identical reference numerals in the individual figures refer toidentical elements or elements with identical function, or elementswhich correspond to one another with regard to their functions.

Specifically, in the figures:

FIG. 1 shows a first exemplary embodiment of a device for opticallysurveillance according to the present invention;

FIG. 2 shows a second exemplary embodiment of the device; and

FIG. 3 shows a third exemplary embodiment of the device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 shows a first exemplary embodiment of a device 110 for opticallysurveilling at least one area 112. In the embodiment of FIG. 1 , thedevice 110 may be designed as light barrier, specifically as one-waylight barrier. The device 110 comprises a sender unit 114 and a receiverunit 116. The sender unit 114 comprises at least one illumination source118. The illumination source 118 may be or may comprise at least onelight source 120. The light source 120 may be or may comprise at leastone multiple beam light source. For example, the light source maycomprise at least one laser source and one or more diffractive opticalelements (DOEs). The illumination source 118 is designed to generate atleast one light beam 122 having a beam profile. Each light beam 122 isdesignated for propagating to the receiver unit 116, thereby traversingat least one area for surveillance 124. The device 110 may be configuredsuch that the light beam 122 propagates from the sender unit 114 towardsthe receiver unit 116 along an optical axis 126 of the device 110.

The device 110 may comprise a connection 128 between the sender unit 114and the receiver unit 116. The connection may be designed for providingsynchronization between the sender unit 144 and the receiver unit 116.The synchronization between the sender unit 114 and the receiver unit116 may be wire bound and/or may be implemented using at least oneoptical synchronization path. Preferably, the connection may be awireless connection such that a wire bound connection is not necessary.The connection 128 may furthermore be configured for tech-in and/orsafety functions.

Specifically, the illumination source 118 may comprise at least onelaser and/or laser source. Various types of lasers may be employed, suchas semiconductor lasers. Additionally or alternatively, non-laser lightsources may be used, such as LEDs and/or light bulbs. The illuminationsource 118 may be adapted to generate and/or to project a cloud ofpoints, for example the illumination source 128 may comprise one or moreof at least one digital light processing projector, at least one LCoSprojector, at least one spatial light modulator; at least onediffractive optical element; at least one array of light emittingdiodes; at least one array of laser light sources. The illuminationsource 118 may comprise an artificial illumination source, in particularat least one laser source and/or at least one incandescent lamp and/orat least one semiconductor light source, for example, at least onelight-emitting diode, in particular an organic and/or inorganiclight-emitting diode. As an example, the light emitted by theillumination source 118 may have a wavelength of 300 to 1000 nm,especially 500 to 1000 nm. Additionally or alternatively, light in theinfrared spectral range may be used, such as in the range of 780 nm to3.0 μm. Specifically, the light in the part of the near infrared regionwhere silicon photodiodes are applicable specifically in the range of700 nm to 1000 nm may be used. On account of their generally definedbeam profiles and other properties of handleability, the use of at leastone laser source as the illumination source is particularly preferred.The illumination source 118 may be integrated into a housing of thedevice 110 for optically surveilling.

The light beam 122 traversing the surveillance area 124 may be lesscollimated, e.g. the light beam may slightly expand with distance fromthe illumination source 118, which allows facilitating the setup of thelight barrier. The sender unit 114 may comprise at least one transferdevice 130 configured for collimating the light beam generated by thelight source 122.

The sender unit 114 further may comprise at least one modulation source132, also denoted as modulation device. The modulation source 132 may beconfigured for generating a modulation pattern in a manner that themodulation source 132 impinges the illumination source 118 to generateat least one light beam carrying the modulation pattern. The modulationpattern may be selected from the group comprising of: a pseudo randommodulation pattern, an Aiken code, a BCD code, a Gillham code, a Stibitzcode, a one-hot code, and a gray code. The modulation pattern may beselected from the group consisting of: a rectangular pulse pattern,50:50 rectangular pattern, sinusoidal pattern, periodic pulse patterns.Compared to the optoelectronic sensor described in DE 10 2016 122 364 A1the sender unit may use more complex modulation patterns to encode thelight source. This may allow that the receiver unit 116 detects thelight beam 122 which was send by the sender unit 114.

The receiver unit 116 comprises at least one transfer device 134. Thetransfer device 134 has at least one focal length in response to the atleast one incident light beam 122 propagating from the illuminationsource 118 to at least two optical sensors 138. The transfer device 134has an optical axis 136. The transfer device 134 constitutes acoordinate system, wherein a longitudinal coordinate I is a coordinatealong the optical axis 136 and wherein d is a spatial offset from theoptical axis 136.

The receiver unit 116 comprises the at least two optical sensors 138.Each optical sensor 138 has at least one light sensitive area 140. Eachoptical sensor 138 is designed to generate at least one sensor signal inresponse to an illumination of its respective light-sensitive area 140by the light beam 122. As shown in FIG. 1 , the light-sensitive areas140 may be oriented towards the sender unit 114, specifically forone-way light barriers. The optical sensors 138 are arranged such thatthe light-sensitive areas 140 of the optical sensors 138 differ in atleast one of: their longitudinal coordinate, their spatial offset, ortheir surface areas. Each light-sensitive area 140 may have ageometrical center.

The optical sensors 138 may be sensitive in one or more of theultraviolet, the visible or the infrared spectral range. Specifically,the optical sensors 138 may be sensitive in the visible spectral rangefrom 500 nm to 780 nm, most preferably at 650 nm to 750 nm or at 690 nmto 700 nm. Specifically, the optical sensors 138 may be sensitive in thenear infrared region. Specifically, the optical sensors 138 may besensitive in the part of the near infrared region where siliconphotodiodes are applicable specifically in the range of 700 nm to 1000nm. The optical sensors 138, specifically, may be sensitive in theinfrared spectral range, specifically in the range of 780 nm to 3.0micrometers. For example, the optical sensors 138 each, independently,may be or may comprise at least one element selected from the groupconsisting of a photodiode, a photocell, a photoconductor, aphototransistor or any combination thereof. For example, the opticalsensors 138 may be or may comprise at least one element selected fromthe group consisting of a CCD sensor element, a CMOS sensor element, aphotodiode, a photocell, a photoconductor, a phototransistor or anycombination thereof. Any other type of photosensitive element may beused. As will be outlined in further detail below, the photosensitiveelement generally may fully or partially be made of inorganic materialsand/or may fully or partially be made of organic materials. Mostcommonly, as will be outlined in further detail below, one or morephotodiodes may be used, such as commercially available photodiodes,e.g. inorganic semiconductor photodiodes. Specifically, thephotosensitive element may be or may comprise at least one elementselected from the group consisting of a photodiode, a photocell, aphotoconductor, a phototransistor or any combination thereof. Any othertype of photosensitive element may be used.

The optical sensors 138 specifically may be semiconductor sensors,preferably inorganic semiconductor sensors, more preferably photodiodesand most preferably silicon photodiodes. Thus, the present inventionsimply may be realized by using commercially available inorganicphotodiodes, i.e. one small photodiode and one large area photodiode.Thus, the setup of the present invention may be realized in a cheap andinexpensive fashion. Specifically, the optical sensors 138 may be or maycomprise inorganic photodiodes which are sensitive in the infraredspectral range, preferably in the range of 780 nm to 3.0 micrometers,and/or sensitive in the visible spectral range, preferably in the rangeof 380 nm to 780 nm. Specifically, the optical sensors 138 may besensitive in the part of the near infrared region where siliconphotodiodes are applicable specifically in the range of 700 nm to 1000nm. Infrared optical sensors which may be used for the optical may becommercially available infrared optical sensors, such as infraredoptical sensors commercially available under the brand name Hertzstueck™from trinamiX GmbH, D-67056 Ludwigshafen am Rhein, Germany. Thus, as anexample, the optical sensors 138 may comprise at least one opticalsensor of an intrinsic photovoltaic type, more preferably at least onesemiconductor photodiode selected from the group consisting of: a Gephotodiode, an InGaAs photodiode, an extended InGaAs photodiode, an InAsphotodiode, an InSb photodiode, a HgCdTe photodiode. Additionally oralternatively, the optical sensors may comprise at least one opticalsensor of an extrinsic photovoltaic type, more preferably at least onesemiconductor photodiode selected from the group consisting of: a Ge:Auphotodiode, a Ge:Hg photodiode, a Ge:Cu photodiode, a Ge:Zn photodiode,a Si:Ga photodiode, a Si:As photodiode. Additionally or alternatively,the optical sensors may comprise at least one at least onephotoconductive sensor such as a PbS or PbSe sensor, a bolometer,preferably a bolometer selected from the group consisting of a VObolometer and an amorphous Si bolometer. The optical sensors 138 may beopaque, transparent or semitransparent. For the sake of simplicity,however, opaque sensors which are not transparent for the light beam,may be used, since these opaque sensors generally are widelycommercially available. The optical sensors 138 specifically may beuniform sensor having a single light-sensitive area 140. The opticalsensors 138 specifically may be non-pixelated optical sensors.Alternatively, one or both of the optical sensors 138 may be pixelatedsensors.

The receiver unit 116 may comprise two optical sensors 138 which may bearranged as follows

-   -   at least one first optical sensor 142 having a first        light-sensitive area 144, wherein the first optical sensor 142        is configured to generate at least one first sensor signal in        response to an illumination of the first light-sensitive area        144 by the light beam 122 propagating from the sender unit 114        to the receiver unit 116; and    -   at least one second optical sensor 146 having a second        light-sensitive area 148, wherein the second optical sensor 146        is configured to generate at least one second sensor signal in        response to an illumination of the second light-sensitive area        148 by the light beam 122, wherein the first light-sensitive        area 144 is smaller than the second light-sensitive area 148.

For example, the surface area of the first light-sensitive area 144 maybe smaller than the surface area of the second light-sensitive area 148,such as by at least a factor of 0.9, e.g. at least a factor of 0.7 oreven by at least a factor of 0.5. As an example, both the firstlight-sensitive area 144 and the second light-sensitive area 148 mayhave the shape of a square or of a rectangle, wherein side lengths ofthe square or rectangle of the first light-sensitive area are smallerthan corresponding side lengths of the square or rectangle of the secondlight-sensitive area. Alternatively, as an example, both the firstlight-sensitive area 144 and the second light-sensitive area 148 mayhave the shape of a circle, wherein a diameter of the firstlight-sensitive area 144 is smaller than a diameter of the secondlight-sensitive area 148. Again, alternatively, as an example, the firstlight-sensitive area may have a first equivalent diameter, and thesecond light-sensitive area may have a second equivalent diameter,wherein the first equivalent diameter is smaller than the secondequivalent diameter.

For example, the optical sensors 138 may be partial diodes of asegmented diode, with a center of the segmented diode being off-centeredfrom the optical axis 136. The optical sensors 138 may be partial diodesof a bi-cell or quadrant diode and/or comprise at least one CMOS sensor.Bi-cell diodes or quadrant diodes are widely commercially available atlow cost, and driving schemes for these bi-cell diodes or quadrantdiodes are generally known. Bi-cell and quadrant diodes may have two orfour separate light sensitive areas 140, in particular two or fouractive areas. As an example, the bi-cell diodes may each formindependent diodes having the full functionality of a diode. As anexample, each of the bi-cell diodes may have a square or rectangularshape, and the two diodes may be placed in one plane such that the twopartial diodes, in total, form a 1×2 or 2×1 matrix having a rectangularshape. Generally, however, the optical sensors 138 specifically may bepartial diodes of a quadrant diode, with a center of the quadrant diodebeing off-centered from the optical axis of the transfer device. As anexample, in a quadrant diode the four partial diodes may each formindependent diodes having the full functionality of a diode. As anexample, the four partial diodes may each have a square or rectangularshape, and the four partial diodes may be placed in one plane such thatthe four partial diodes, in total, form a 2×2 matrix having arectangular or square shape. In a further example, the four partialdiodes, in total, may form a 2×2 matrix having a circular or ellipticalshape. The partial diodes, as an example, may be adjacent, with aminimum separation from one another. As an example, the center of thebi-cell diodes, which may be an intersection of the geometrical centersof the optical sensors of the bi-cell diode, may be off-centered fromthe optical axis by at least 0.01 mm, more preferably by at least 0.1mm, more preferably by at least 1.0 mm or even 2.0 mm. Thus, as afurther example, the center of the center of the bi-cell diodes may beoff-centered from the optical axis by a factor of at least 0.0001 timesthe maximum extent of the light sensitive area orthogonal to the opticalaxis, preferably by a factor of at least 0.001, more preferably by afactor of at least 0.005 times the maximum extent of the light sensitivearea orthogonal to the optical axis.

In case a quadrant diode is used, having a 2×2 matrix of partial diodes,the center of the quadrant diode specifically may be off-centered oroffset from the optical axis of the transfer device of the receiverunit. Thus, as an example, the center of the quadrant diodes, which maybe an intersection of the geometrical centers of the optical sensors ofthe quadrant diode, may be off-centered from the optical axis by atleast 0.1 mm, more preferably by at least 0.5 mm, more preferably by atleast 1.0 mm or even 2.0 mm. Thus, as a further example, the center ofthe center of the quadrant diodes may be off-centered from the opticalaxis by a factor of at least 0.0001 times the maximum extent of thelight sensitive area orthogonal to the optical axis, preferably by afactor of at least 0.001, more preferably by a factor of at least 0.005times the maximum extent of the light sensitive area orthogonal to theoptical axis. Similarly, when using other types of optical sensorssetups having a plurality of optical sensors 138, an overall center ofthe optical sensors 138 may be offset from the optical axis by the samedistance. Generally, the light-sensitive areas 140 of the opticalsensors 138 may have an arbitrary surface area or size. Preferably,however, specifically in view of a simplified evaluation of the sensorsignals, the light-sensitive areas of the optical sensors aresubstantially equal, such as within a tolerance of less than 10%,preferably less than 5% or even less than 1%. This, specifically, is thecase in typical commercially available quadrant diodes. As an example,commercially available quadrant photodiodes may be integrated in orderto provide four optical sensors 138, such as one or more quadrantphotodiodes available from Hamamatsu Photonics Deutschland GmbH, D-82211Herrsching am Ammersee, Germany, such as quadrant Si PIN photodiodes ofthe type S4349, which are sensitive in the UV spectral range to the nearIR spectral range. In case an array of optical sensors is used, thearray may be a naked chip or may be an encapsulated array, such asencapsulated in a TO-5 metal package. Additionally or alternatively, asurface mounted device may be used, such as TT Electronics OPR5911available from TT Electronics plc, Fourth Floor, St Andrews House, WestStreet Woking Surrey, GU21 6EB, England. It shall be noted that otheroptical sensors may also be used.

For example, the receiver unit may comprise at least one sensor elementhaving a matrix of optical sensors 138, the optical sensors 138 eachhaving a light-sensitive area. Each optical sensor 138 may be configuredto generate at least one sensor signal in response to an illumination ofthe light-sensitive area 140 by the light beam 122 propagating from thesender unit 114 to the receiver unit 116. The matrix may be or maycomprise a rectangular matrix having one or more rows and one or morecolumns. The rows and columns specifically may be arranged in arectangular fashion. It shall be outlined, however, that otherarrangements are feasible, such as nonrectangular arrangements. As anexample, circular arrangements are also feasible, wherein the elementsare arranged in concentric circles or ellipses about a center point. Forexample, the matrix may be a single row of pixels. Other arrangementsare feasible. The optical sensors 138 of the matrix specifically may beequal in one or more of size, sensitivity and other optical, electricaland mechanical properties. The light-sensitive areas 140 of all opticalsensors of the matrix specifically may be located in a common plane, thecommon plane preferably facing the sender unit, such that the light beampropagating from the sender unit 114 to the receiver unit 116 maygenerate a light spot on the common plane. As outlined above, theoptical sensors specifically may be or may comprise photodetectors,preferably inorganic photodetectors, more preferably inorganicsemiconductor photodetectors, most preferably silicon photodetectors.Specifically, the optical sensors may be sensitive in the infraredspectral range. All of the optical sensors 138 of the matrix or at leasta group of the optical sensors 138 of the matrix specifically may beidentical. Groups of identical optical sensors 138 of the matrixspecifically may be provided for different spectral ranges, or alloptical sensors may be identical in terms of spectral sensitivity.Further, the optical sensors 138 may be identical in size and/or withregard to their electronic or optoelectronic properties. The matrix maybe composed of independent optical sensors 138. Thus, a matrix ofinorganic photodiodes may be composed. Alternatively, however, acommercially available matrix may be used, such as one or more of a CCDdetector, such as a CCD detector chip, and/or a CMOS detector, such as aCMOS detector chip. Thus, generally, the optical sensors 138 may form asensor array or may be part of a sensor array, such as theabove-mentioned matrix. Thus, as an example, the receiver unit 116 maycomprise an array of optical sensors 138, such as a rectangular array,having m rows and n columns, with m, n, independently, being positiveintegers. Preferably, more than one column and more than one row isgiven, i.e. n>1, m>1. Thus, as an example, n may be 2 to 16 or higherand m may be 2 to 16 or higher. Preferably, the ratio of the number ofrows and the number of columns is close to 1. As an example, n and m maybe selected such that 0.3 s m/n s 3, such as by choosing m/n=1:1, 4:3,16:9 or similar. As an example, the array may be a square array, havingan equal number of rows and columns, such as by choosing m=2, n=2 orm=3, n=3 or the like. The matrix specifically may be a rectangularmatrix having at least one row, preferably a plurality of rows, and aplurality of columns. As an example, the rows and columns may beoriented essentially perpendicular. Thus, as an example, tolerances ofless than 20°, specifically less than 10° or even less than 5°, may beacceptable. In order to provide a wide range of view, the matrixspecifically may have at least 10 rows, preferably at least 50 rows,more preferably at least 100 rows. Similarly, the matrix may have atleast 10 columns, preferably at least 50 columns, more preferably atleast 100 columns. The matrix may comprise at least 50 optical sensors138, preferably at least 100 optical sensors 138, more preferably atleast 500 optical sensors 138. The matrix may comprise a number ofpixels in a multi-mega pixel range. Other embodiments, however, arefeasible.

The receiver unit 114 comprises at least one evaluation device 150. Theevaluation device 150 is configured for generating an output bymonitoring at least one change of, firstly, the beam profile of the atleast one light beam 122 upon traversing the at least one area ofsurveillance 124 by evaluating the sensor signals and, further, of atleast one component of a location of the sender unit 116, wherein thecomponent is determined with respect to the coordinate system of thetransfer device 134, by evaluating a combined signal Q from the sensorsignals.

The evaluation device 150 may be configured for generating the outputbased on the distance by photon ratio (DPR) technique which is describede.g. in WO 2018/091649 A1, WO 2018/091638 A1 and WO 2018/091640, thecontent of which is included by reference. The DPR technique allowsdistance measurements such as determining a longitudinal coordinate ofthe sender unit. In addition, the DPR technique also allows recognizinggeometrical changes to the light beam 122 upon traversing the area ofsurveillance 124 such as partial coverage of the light beam 122. Thecombined signal Q may be generated by combining the sensor signals, inparticular by one or more of dividing the sensor signals, dividingmultiples of the sensor signals or dividing linear combinations of thesensor signals. In particular, the combined signal may be a quotientsignal. The combined signal Q may be determined by using various means.As an example, a software means for deriving the combined signal, ahardware means for deriving the combined signal, or both, may be usedand may be implemented in the evaluation device. Thus, the evaluationdevice 150, as an example, may comprise at least one divider 152,wherein the divider is configured for deriving the combined signal. Thedivider 152 may fully or partially be embodied as one or both of asoftware divider or a hardware divider.

The evaluation device may be configured for deriving the combined signalQ by one or more of dividing the sensor signals, dividing multiples ofthe sensor signals, dividing linear combinations of the sensor signals.The evaluation device may be configured for using at least onepredetermined relationship between the combined signal Q and thelongitudinal coordinate for determining the longitudinal coordinate. Thedetermining of the at least one longitudinal coordinate of the senderunit may be performed by the at least one evaluation device. Thus, as anexample, the relationship may be implemented in software and/orhardware, such as by implementing one or more lookup tables. Thus, as anexample, the evaluation device may comprise one or more programmabledevices such as one or more computers, application-specific integratedcircuits (ASICs), Digital Signal Processors (DSPs), or FieldProgrammable Gate Arrays (FPGAs) which are configured to perform theabove-mentioned evaluation, in order to determine the at least onelongitudinal coordinate of the sender unit. Additionally oralternatively, however, the evaluation device may also fully orpartially be embodied by hardware.

For example, the evaluation device 150 may be configured for derivingthe combined signal Q by

${Q\left( z_{O} \right)} = \frac{\underset{A_{1}}{\int\int}{E\left( {x,{y;z_{O}}} \right)}{dxdy}}{\underset{A_{2}}{\int\int}{E\left( {x,y,z_{O}} \right)}{dxdy}}$

-   -   wherein x and y are transversal coordinates, A1 and A2 are areas        of the beam profile of the light beam 122 at the position of the        optical sensors 138, and E(x,y,z_(o)) denotes the beam profile        for the distance of the sender unit z_(o). Area A1 and area A2        may differ. In particular, A1 and A2 are not congruent. Thus, A1        and A2 may differ in one or more of the shape or content. The        beam profile may be a cross section of the light beam 122. The        beam profile may be selected from the group consisting of a        trapezoid beam profile; a triangle beam profile; a conical beam        profile and a linear combination of Gaussian beam profiles. Each        of the sensor signals may comprise at least one information of        at least one area of the beam profile of the light beam. The        light-sensitive areas 140 may be arranged such that a first        sensor signal comprises information of a first area of the beam        profile and a second sensor signal comprises information of a        second area of the beam profile. The first area of the beam        profile and second area of the beam profile may be one or both        of adjacent or overlapping regions. The first area of the beam        profile and the second area of the beam profile may be not        congruent in area.

The evaluation device 150 may be configured to determine and/or toselect the first area of the beam profile and the second area of thebeam profile. The first area of the beam profile may compriseessentially edge information of the beam profile and the second area ofthe beam profile may comprise essentially center information of the beamprofile. The beam profile may have a center, i.e. a maximum value of thebeam profile and/or a center point of a plateau of the beam profileand/or a geometrical center of the light spot, and falling edgesextending from the center. The second region may comprise inner regionsof the cross section and the first region may comprise outer regions ofthe cross section. Preferably the center information has a proportion ofedge information of less than 10%, more preferably of less than 5%, mostpreferably the center information comprises no edge content. The edgeinformation may comprise information of the whole beam profile, inparticular from center and edge regions. The edge information may have aproportion of center information of less than 10%, preferably of lessthan 5%, more preferably the edge information comprises no centercontent. At least one area of the beam profile may be determined and/orselected as second area of the beam profile if it is close or around thecenter and comprises essentially center information. At least one areaof the beam profile may be determined and/or selected as first area ofthe beam profile if it comprises at least parts of the falling edges ofthe cross section. For example, the whole area of the cross section maybe determined as first region. The first area of the beam profile may bearea A2 and the second area of the beam profile may be area A1.

The edge information may comprise information relating to a number ofphotons in the first area of the beam profile and the center informationmay comprise information relating to a number of photons in the secondarea of the beam profile. The evaluation device 150 may be adapted fordetermining an area integral of the beam profile. The evaluation device150 may be adapted to determine the edge information by integratingand/or summing of the first area. The evaluation device 150 may beadapted to determine the center information by integrating and/orsumming of the second area. For example, the beam profile may be atrapezoid beam profile and the evaluation device may be adapted todetermine an integral of the trapezoid. Further, when trapezoid beamprofiles may be assumed, the determination of edge and center signalsmay be replaced by equivalent evaluations making use of properties ofthe trapezoid beam profile such as determination of the slope andposition of the edges and of the height of the central plateau andderiving edge and center signals by geometric considerations.

Additionally or alternatively, the evaluation device 150 may be adaptedto determine one or both of center information or edge information fromat least one slice or cut of the light spot. This may be realized, forexample, by replacing the area integrals in the combined signal Q byline integrals along the slice or cut. For improved accuracy, severalslices or cuts through the light spot may be used and averaged. In caseof an elliptical spot profile, averaging over several slices or cuts mayresult in an improved distance information.

The evaluation device 150 may be configured to derive the combinedsignal Q by one or more of dividing the edge information and the centerinformation, dividing multiples of the edge information and the centerinformation, dividing linear combinations of the edge information andthe center information. Thus, essentially, photon ratios may be used asthe physical basis of the method. The evaluation device 150 may beconfigured for determining the longitudinal coordinate by evaluating thecombined signal Q. The evaluation device 150 may be configured for usingat least one predetermined relationship between the combined signal Qand the longitudinal coordinate. The predetermined relationship may beone or more of an empiric relationship, a semi-empiric relationship andan analytically derived relationship. The evaluation device 150 maycomprise at least one data storage device for storing the predeterminedrelationship, such as a lookup list or a lookup table.

The combined signal Q can be used for determining manipulations such aswillful and/or not intentional manipulations. The manipulation may be anarbitrary willful and/or not intentional intervention into the device110 resulting in a change of one property of the light beam 122 such asa change of a length and/or direction of the beam path. The beam pathfrom the sender unit 114 to the receiver unit 116 may change due tochanges in the optical system such as due to one or more of water,scratches, introducing additional reflective elements, dirt, or evenfalseful arrangement of the components of the light barrier.Specifically, such changes may lead to a change in one or more of x-,y-, or z-position of the sender unit 114, the beam profile, the combinedsignal Q and the sensor signals of the optical sensors 138. Changes of alength of the beam path may be detectable by monitoring the combinedsignal Q, specifically changes of the combined signal Q. The combinedsignal Q can be used for determining a z-position of the sender unit. Asthe combined signal Q depends on the beam profile of the light beam 122,the combined signal Q can be used for determining changes in the beamprofile. The evaluation device 150 may be configured to determinechanges in the length of the beam path by determining and evaluating thecombined signal Q as described e.g. in WO 2018/091649 A1, WO 2018/091638A1 and WO 2018/091640 A1. The evaluation device 150 may be configuredfor monitoring the combined signal Q and for determining changes of thecombined signal Q. The evaluation device may be configured fordetermining a manipulation based the determined change. For example, theevaluation device may be adapted for determining the longitudinalcoordinate of the sender unit by evaluating the combined signal Q. Incase the z-position of the sender unit was changed, e.g. by introducingadditional reflective elements, the evaluation of the combined signal Qwill result in a longitudinal coordinate which is different from areference longitudinal coordinate. The evaluation device 150 may beconfigured for comparing the reference longitudinal coordinate and themeasured longitudinal coordinate. The evaluation device 150 may beconfigured for indicating a manipulation if the reference longitudinalcoordinate and the measured longitudinal coordinate differ, whereindifferences within a tolerance range may be tolerated. Manipulationsfurther may result in a change of the x- and/or y-position of the lightbeam impinges on the respective optical sensor and, thus, to changes ofcoverage, such as a partial coverage, of the light sensitive area 140 ofthe respective optical sensor 138. The combined signal Q can be used fordetecting these geometrical changes of the light beam. Specifically, theevaluation device 150 may be configured for determining a change of theat least one transversal coordinate x and/or y of the sender unit bydetecting geometrical changes of the light beam 122, such as bymonitoring simultaneously the position of the center of gravity of thelight spot and the total intensity of the light spot, whereas a changein at least one transversal coordinate x and/or y is likely in case thecenter of gravity position changes, while the total intensity of thelight spot is unchanged. A combination of monitoring several parameterssuch as monitoring of the z-position in combination with monitoring thex- and/or y-position may allow enhancing reliability of the lightbarrier. The output may be an arbitrary indication about a change of amonitored parameter such as the beam profile of the light beam upontraversing the at least one area and/or of the at least one component ofthe location of the sender unit. The output may be and/or may compriseat least one output signal. The output may comprise at least one binarysignal indicating whether or not a change is present. The output maycomprise at least one information about the change such as an amount ofdifference, which parameter is changed, which parameter were monitoredor the like.

The evaluation device 150 may further be designed for generating the atleast one output by monitoring a change of the sensor signals of theoptical sensors 138. The evaluation device 150 may be designed forgenerating the output by using at least one reference beam profile forthe at least one light beam 122 generated by the illumination source 118and at least one reference component for the at least one component ofthe location of the sender unit 114. One or more reference parameterselected from the group consisting of the reference beam profile, thereference component of location, the reference sensor signals, thereference combined signal Q may be pre-determined and/or pre-defined.The at least one reference beam profile and/or the at least onereference component of the location of the sender unit 114 and/or thereference sensor signals and/or the reference combined signal Q may bestored during a teaching phase. The evaluation device 150 may compriseat least one storage unit in which one or more of the reference beamprofile, the reference component of location, the reference sensorsignals, the reference combined signal Q may be stored such as in atable or lookup table.

The evaluation device 150 may be configured to compare the monitoredparameter with the respective reference parameter. A change may bedetermined by using at least one mathematical operation such assubtracting the respective reference value or profile from thedetermined value or profile or vice versa, respectively. The evaluationdevice 150 may be configured to determine if the difference between thereference parameter and the monitored parameter exceeds at least onethreshold value and in case the difference exceeds the threshold toindicate a change. Manipulations may be defined as changes in one ormore of x-, y-, or z-position, the combined signal Q and the sensorsignals of the optical sensors 138, specifically, if the change concernsone optical sensor 138 while the other sensor signal remains unchanged.

The combination of several surveillance parameters such as beam profile,combined signal Q, sensor signals, at least one component of locationmay allow providing a light barrier with enhanced reliability againstmanipulations. Specifically, the light barrier may be more reliableagainst reflections from highly reflective environment such as metalsheets or surfaces. Information from the beam profile or the x-yposition may be used for safety monitoring functions. As an example,changes of the beam profile may also indicate dirt on the optical systemthat may cause a failure of the safety function. Further, exhaust gases,steam, or particle emissions that may cause a failure of the system mayalso be detected by monitoring the beam profile. Monitoring thez-positions such as the longitudinal coordinate of the sender unit 114may also allow recognizing a shortening of the distance the light issupposed to have traveled. This may indicate a change in the opticalsystem such as due to water, scratches, manipulations, or dirt, or itmay indicate a falseful reassembly of the light barrier.

The evaluation device 150 may be configured for initiating at least oneaction based on the output, wherein the at least one action is selectedfrom at least one of: providing at least one information such as asafety function, generating at least one warning, inducing at least oneinstruction, changing an output signal. Specifically, the evaluationdevice actuates at least one safety function based on the output. Theinformation may be a warning, a safe-shutdown, an emergency warning, aviolation information or the like. The evaluation device 150 may beconfigured for assigning the information to a time of event and forstoring a combination of the information with the time of event in aninformation log. The warning may comprise a visual, an audible or ahaptic warning signal. The instruction may comprise initiating ashutdown of at least one apparatus, such as of a machine. The evaluationdevice 150 may be configured that not every change in one of themonitored parameters may lead to a shutdown and/or warning and/or changeof an output signal, but may lead in each case to an information aboutthe origin of the change such as the changed parameter.

The evaluation device 150 may comprise at least one safety unit 154comprising at least one electrosensitive protective equipment (ESPE)156. The ESPE may comprise a plurality of elements which are configuredfor protective tripping and/or presence sensing purposes such as asensing function and/or a control or monitoring function. Specifically,the ESPE may comprise at least one output signal switching device (OSSD)158. The OSSD 158 may be connected to a machine control system of anapparatus. In case the evaluation device has actuated the safetyfunction, specifically has initiated the action as described above, themachine control system responds by going into a safe state such as anOFF state. The apparatus may comprise one or more of at least oneelectrically powered machine primary control element (MPCE) configuredfor controlling normal operation of the apparatus, at least one machinesecondary control element (MSCE) which is a further machine controlelement configured for removing power source from prime mover ofhazardous parts, at least one final switching device (FSD), at least onesecondary switching device (SSD), normally closed (NC) contacts andnormally open (NO) contacts. The FSD may be configured in response tothe indication from the OSSD 158 to interrupt the circuit connecting themachine control system to the machine primary control system. In thissituation, the SSD may be configured for performing a back-up functionby going to the OFF state and initiating further machine control actionssuch as de-energizing the MSCE.

Using the DPR technique may be advantageous since it is possible to usecommonplace and cheap Si-sensors such as bi-cells or quadrant diodesthat are much faster and have a larger bandwidth than for example FiPsensors. Further Si-sensors may be more homogeneous and entirelyintensity independent, whereas in FiP devices homogeneity requirementscan make fabrication costly and intensity independence of the FiPquotient requires additional technical effort. For possible embodimentsof sensors using DPR technique reference is made to WO 2018/091649 A1,WO 2018/091638 A1 and WO 2018/091640 A1, the content of which isincluded by reference.

FIG. 2 shows an embodiment of the device 110, wherein the device 110 isdesigned as reflective light barrier. In this embodiment the sender unit114 and the light-sensitive areas 140 of the optical sensors 138 may beoriented towards a reflective target 159. Thus, the reflective target159, sender unit 114 and receiver unit 116 may be arranged such that thelight beam 122 propagates from the sender unit 114 to the reflectivetarget 159 and such that the light beam is reflected by the reflectivetarget 159 to the receiver unit 116. With respect to embodiments anddesign of the sender unit 114 and receiver unit 116 reference is made tothe description of FIG. 1 above.

FIG. 3 shows an embodiment of the device 110, wherein the device 110 isdesigned as light curtain. The device 110 may comprise a plurality ofsender units 114 and/or receiver units 116. With respect to embodimentsand design of the sender unit 114 and receiver unit 116 reference ismade to the description of FIG. 1 above. The receiver units 116 may beconfigured to detect the light beams 122 having traversed the area ofsurveillance 124 of more than one sender unit 114 simultaneously ornon-simultaneously. To ensure safe operation, the receiver unit 116 maybe configured to monitor the presence of the light beam 122 and/or thebeam profile and/or at least one of x-position, y-position, z-positionof each sender unit 114 and send out an information in case of a change.In case of a plurality of receiver units 114 each receiver unit 114 maycomprise a separate evaluation device 150 and/or the receiver units 114may comprise a central evaluation device 160 which may be configured toevaluate the sensor signals of each of the receiver units using forexample a multiplexing scheme.

The sender units 114 each may comprise at least one illumination sources118. Each of the illumination sources 118 may be designed for beingmodulated by an individual modulation pattern, the individual modulationpattern may be different with respect to each other. The sender units114 each may comprise an individual modulation source 132 for eachillumination source 118, or wherein the sender units 114 furthercomprises a central modulation device 162 comprising a multiplexer beingdesignated for switching an individual impingement of the illuminationsources by a single modulation source. The evaluation devices 150,specifically the central evaluation device 160, is designated forassigning an individual modulation pattern to an individual illuminationsource 118.

LIST OF REFERENCE NUMBERS

-   -   110 device for optical surveillance    -   112 area    -   114 sender unit    -   116 receiver unit    -   118 illumination source    -   120 light source    -   122 light beam    -   124 area of surveillance    -   126 optical axis    -   128 connection    -   130 transfer device    -   132 modulation source    -   134 transfer device    -   136 optical axis    -   138 optical sensor    -   140 light-sensitive area    -   142 first optical sensor    -   144 first light-sensitive area    -   146 second optical sensor    -   148 second light-sensitive area    -   150 evaluation device    -   152 divider    -   156 ESPE    -   158 OSSD    -   159 reflective target    -   160 central evaluation device    -   162 central modulation device

1. A device (110) for optically surveilling at least one area (112), thedevice (110) comprising a sender unit (114) and a receiver unit (116),wherein the sender unit (114) has at least one illumination source(118), wherein the illumination source (118) is designed to generate atleast one light beam (122) having a beam profile, wherein each lightbeam (122) is designated for propagating to the receiver unit (116),thereby traversing at least one area for surveillance (124); wherein thereceiver unit (116) comprises: at least one transfer device (134),wherein the transfer device (134) has at least one focal length inresponse to the at least one incident light beam (122) propagating fromthe illumination source (118) to at least two optical sensors (138),wherein the transfer device (134) has an optical axis (136), wherein thetransfer device (134) constitutes a coordinate system, wherein alongitudinal coordinate I is a coordinate along the optical axis andwherein d is a spatial offset from the optical axis (136); the at leasttwo optical sensors (138), wherein each of the at least two opticalsensors (138) has at least one light sensitive area (140), wherein eachoptical sensor (138) is designed to generate at least one sensor signalin response to an illumination of its respective light-sensitive area(140) by the light beam (122), wherein two of the optical sensors (138)are arranged in a manner that the light-sensitive areas (140) of the twooptical sensors (138) differ in at least one of: their longitudinalcoordinate, their spatial offset, or their surface areas; and at leastone evaluation device (150), wherein the evaluation device (150) isconfigured for generating an output by monitoring at least one changeof, firstly, the beam profile of the at least one light beam (122) upontraversing the at least one area of surveillance (124) by evaluating thesensor signals and, further, of at least one component of a location ofthe sender unit (114), wherein the component is determined with respectto the coordinate system of the transfer device (134), by evaluating acombined signal Q from the sensor signals.
 2. The device (110) accordingto claim 1, wherein the evaluation device (150) is further configuredfor initiating at least one action based on the output, wherein the atleast one action is selected from the group consisting of providing atleast one information, generating at least one warning, inducing atleast one instruction, and changing an output signal.
 3. The device(110) according to claim 2, wherein the evaluation device (150) isfurther configured for assigning the information to a time of event andfor storing a combination of the information with the time of event inan information log.
 4. The device (110) according to claim 2, whereinthe warning comprises a visual, an audible or a haptic warning signal.5. The device (110) according to claim 2, wherein the instructioncomprises initiating a shutdown of at least one apparatus.
 6. The device(110) according to claim 1, wherein the sender unit (114) furthercomprises at least one modulation source (132), the modulation source(132) being configured for generating a modulation pattern in a mannerthat the modulation source (132) impinges the illumination source (118)to generate at least one light beam (122) carrying the modulationpattern.
 7. The device (110) according to claim 6, wherein themodulation pattern is selected from the group consisting of: a pseudorandom modulation pattern, an Aiken code, a BCD code, a Gillham code, aStibitz code, a one-hot code, and a gray code.
 8. The device (110)according to claim 6, wherein the sender unit (114) comprises at leasttwo illumination sources (118), wherein each of the illumination sources(118) is designed for being modulated by an individual modulationpattern, the individual modulation pattern of two illumination sources(118) being different with respect to each other.
 9. The device (110)according to claim 6, wherein the sender unit (114) comprises anindividual modulation source (132) for each illumination source (118),or wherein the sender unit (114) further comprises a multiplexerdesignated for switching an individual impingement of at least two ofthe illumination sources (118) by a single modulation source (132). 10.The device (110) according to claim 8, wherein the evaluation device(150) is designated for assigning an individual modulation pattern to anindividual illumination source (118).
 11. The device (110) according toclaim 1, further comprising a connection (128) between the sender unit(114) and the receiver unit (116), wherein the connection (128) isdesigned for providing synchronization between the sender unit (114) andthe receiver unit (116).
 12. The device (110) according to claim 1,further comprising at least one reflective target (159) designed forbeing impinged by the at least one light beam (122) propagating from theat least one illumination source (118) to the at least two opticalsensors (138).
 13. The device (110) according to claim 1, wherein two ofthe optical sensors (138) are arranged as: at least one first opticalsensor (142) having a first light-sensitive area (144), wherein thefirst optical sensor (142) is configured to generate at least one firstsensor signal in response to an illumination of the firstlight-sensitive area (144) by the light beam (122) propagating from thesender unit (114) to the receiver unit (116); and at least one secondoptical sensor (146) having a second light-sensitive area (148), whereinthe second optical sensor (146) is configured to generate at least onesecond sensor signal in response to an illumination of the secondlight-sensitive area (148) by the light beam (122), wherein the firstlight-sensitive area (144) is smaller than the second light-sensitivearea (148); wherein the evaluation device (150) is configured forgenerating the output by evaluating the first and second sensor signals.14. The device (110) according to claim 13, wherein the evaluationdevice (150) is further designed for generating the at least one outputby monitoring a change of the first sensor signal or of the secondsensor signal.
 15. The device (110) according to claim 1, wherein thesender unit (114) and the receiver unit (116) are arranged with respectto each other in a manner that the sensor signal of at least one of theoptical sensors is a highest sensor signal.
 16. The device (110)according to claim 1, wherein the evaluation device (150) is furtherdesigned for generating the output by using at least one reference beamprofile for the at least one light beam generated by the illuminationsource (118) and at least one reference component for the at least onecomponent of the location of the sender unit (114).
 17. The device (110)according to claim 16, wherein the at least one reference beam profileand the at least one reference component are stored during a teachingphase.
 18. A method for optically surveilling at least one area by usingat least one device comprising a sender unit (114) and a receiver unit(116), the method comprising the following steps: providing a senderunit (114) having at least one illumination source (118), wherein theillumination source (118) is designed to generate at least one lightbeam (122), each light beam (122) having a beam profile, wherein eachlight beam (122) is designated for propagating to the receiver unit(116), thereby traversing the at least one area for surveillance (124);providing a receiver unit (116) having at least one transfer device(134), at least two optical sensors (138) and an evaluation device(150), wherein the transfer device (134) has at least one focal lengthin response to the at least one incident light beam (122) propagatingfrom the illumination source (118) to at least two optical sensors(138), wherein the transfer device (134) has an optical axis (136),wherein the transfer device (134) constitutes a coordinate system,wherein a longitudinal coordinate I is a coordinate along the opticalaxis (136) and wherein d is a spatial offset from the optical axis(136), wherein each optical sensor (138) has at least one lightsensitive area (140), wherein each optical sensor (138) is designed togenerate at least one sensor signal in response to an illumination ofits respective light-sensitive area (140) by the light beam (122),wherein two of the optical sensors (138) are arranged in a manner thatthe light-sensitive areas (140) of the two optical sensors (138) differin at least one of: their longitudinal coordinate, their spatial offset,or their surface areas; generating the at least one light beam (122) forilluminating each of the light-sensitive areas (140) of the at least twooptical sensors (138) of the receiver unit (116) with the light beam(122) propagating from the sender unit (114) to the receiver unit (116),thereby traversing at least one area for surveillance (124), wherein,thereby, each of the light-sensitive areas (140) generates at least onesensor signal; and evaluating the sensor signals, thereby, generating anoutput by monitoring at least one change of, firstly, the beam profileof the at least one light beam (122) upon traversing the at least onearea of surveillance (124) by evaluating the sensor signals and,further, of at least one component of a location of the sender unit(114), wherein the component is determined with respect to thecoordinate system of the transfer device (134), by evaluating a combinedsignal Q from the sensor signals.
 19. The method according to claim 18,further comprising initiating at least one action based on the output,wherein the at least one action is selected from the group consisting ofproviding at least one information, generating at least one warning,inducing at least one instruction, and changing an output signal.
 20. Amethod of using the device (110) according to claim 1, the methodcomprising using the device (110) for a purpose selected from the groupconsisting of: monitoring at least one apparatus located in asurveillance area; distinguishing between a willful manipulation from anot intentional manipulation related to the at least one apparatuslocated in the surveillance area; and indicating a failure of a safetyfunction.